Frac Plug

ABSTRACT

A plug apparatus comprises a wedge, a sealing ring, and a slip. The wedge comprises an axial wedge bore. A seat is defined in the wedge bore. The seat is adapted to receive a ball. The wedge has a tapered outer surface which decreases in diameter from the upper to the lower extent of the tapered outer surface. The sealing ring is received around the tapered outer surface of the wedge. The sealing ring has an axial ring bore and is radially expandable. The slip comprises an axial slip bore having a tapered inner surface. The tapered inner surface decreases in diameter from the upper to the lower extent of the tapered inner surface. The inner surface is adapted to receive the wedge. The wedge is adapted for displacement from an unset position generally above the slip to a set position wherein the wedge is received in the slip bore.

CLAIM TO PRIORITY

This application is a continuation of a non-provision patent applicationentitled “Frac Plug”, U.S. Ser. No. 15/414,378, filed Jan. 24, 2017,which is a continuation-in-part of a non-provisional patent applicationentitled “Frac Plug”, U.S. Ser. No. 15/055,696, filed Feb. 29, 2016,which claims priority of a provisional patent application entitled “FracPlug”, U.S. Ser. No. 62/149,553, filed Apr. 18, 2015, the disclosure anddrawings of which applications are incorporated herein in their entiretyby reference.

FIELD OF THE INVENTION

The present invention relates generally to plugs that may be used toisolate a portion of a well, and more particularly, to plugs that may beused in fracturing or other processes for stimulating oil and gas wells.

BACKGROUND OF THE INVENTION

Hydrocarbons, such as oil and gas, may be recovered from various typesof subsurface geological formations. The formations typically consist ofa porous layer, such as limestone and sands, overlaid by a nonporouslayer. Hydrocarbons cannot rise through the nonporous layer, and thus,the porous layer forms an area or reservoir in which hydrocarbons areable to collect. A well is drilled through the earth until thehydrocarbon bearing formation is reached. Hydrocarbons then are able toflow from the porous formation into the well.

In what is perhaps the most basic form of rotary drilling methods, adrill bit is attached to a series of pipe sections referred to as adrill string. The drill string is suspended from a derrick and rotatedby a motor in the derrick. A drilling fluid or “mud” is pumped down thedrill string, through the bit, and into the well bore. This fluid servesto lubricate the bit and carry cuttings from the drilling process backto the surface. As the drilling progresses downward, the drill string isextended by adding more pipe sections.

When the drill bit has reached the desired depth, larger diameter pipes,or casings, are placed in the well and cemented in place to prevent thesides of the borehole from caving in. Cement is introduced through awork string. As it flows out the bottom of the work string, fluidsalready in the well, so-called “returns,” are displaced up the annulusbetween the casing and the borehole and are collected at the surface.

Once the casing is cemented in place, it is perforated at the level ofthe oil bearing formation to create openings through which oil can enterthe cased well. Production tubing, valves, and other equipment areinstalled in the well so that the hydrocarbons may flow in a controlledmanner from the formation, into the cased well bore, and through theproduction tubing up to the surface for storage or transport.

This simplified drilling and completion process, however, is rarelypossible in the real world. Hydrocarbon bearing formations may be quitedeep or otherwise difficult to access. Thus, many wells today aredrilled in stages. An initial section is drilled, cased, and cemented.Drilling then proceeds with a somewhat smaller well bore which is linedwith somewhat smaller casings or “liners.” The liner is suspended fromthe original or “host” casing by an anchor or “hanger.” A seal also istypically established between the liner and the casing and, like theoriginal casing, the liner is cemented in the well. That process thenmay be repeated to further extend the well and install additionalliners. In essence, then, a modern oil well typically includes a numberof tubes telescoped wholly or partially within other tubes.

Moreover, hydrocarbons are not always able to flow easily from aformation to a well. Some subsurface formations, such as sandstone, arevery porous. Hydrocarbons are able to flow easily from the formationinto a well. Other formations, however, such as shale rock, limestone,and coal beds, are only minimally porous. The formation may containlarge quantities of hydrocarbons, but production through a conventionalwell may not be commercially practical because hydrocarbons flow thoughthe formation and collect in the well at very low rates. The industry,therefore, relies on various techniques for improving the well andstimulating production from formations. In particular, varioustechniques are available for increasing production from formations whichare relatively nonporous.

One technique involves drilling a well in a more or less horizontaldirection, so that the borehole extends along a formation instead ofpassing through it. More of the formation is exposed to the borehole,and the average distance hydrocarbons must flow to reach the well isdecreased. Another technique involves creating fractures in a formationwhich will allow hydrocarbons to flow more easily. Indeed, thecombination of horizontal drilling and fracturing, or “frac'ing” or“Tracking” as it is known in the industry, is presently the onlycommercially viable way of producing natural gas from the vast majorityof North American gas reserves.

Fracturing a formation is accomplished by pumping fluid, most commonlywater, into the well at high pressure and flow rates. The fluid isinjected into the formation, fracturing it and creating flow paths tothe well. Proppants, such as grains of sand, ceramic or otherparticulates, usually are added to the frac fluid and are carried intothe fractures. The proppant serves to prevent fractures from closingwhen pumping is stopped.

Fracturing typically involves installing a production liner in theportion of the well bore which passes through the hydrocarbon bearingformation. The production liner may incorporate valves, typicallysliding sleeve valves, which may be actuated to open ports in the valve.The valves also incorporate a plug. The plug restricts flow through theliner and diverts it through the valve ports and into the formation.Once fracturing is complete various operations will be performed to“unplug” the valve and allow fluids from the formation to enter theliner and travel to the surface.

In many wells, however, the production liner does not incorporatevalves. Instead, fracturing will be accomplished by “plugging andperfing” the liner. In a “plug and perf” job, the production liner ismade up from standard lengths of liner. The liner does not have anyopenings through its sidewalls, nor does it incorporate frac valves. Itis installed in the well bore, and holes then are punched in the linerwalls. The perforations typically are created by so-called “perf” gunswhich discharge shaped charges through the liner and, if present,adjacent cement.

A plug and perf operation can allow a well to be fractured at manydifferent locations, but rarely, if ever, will the well be fractured allat once. The liner typically will be perforated first in a zone near thebottom of the well. Fluids then are pumped into the well to fracture theformation in the vicinity of the bottom perforations.

After the initial zone is fractured, a plug is installed in the liner ata point above the fractured zone. The liner is perforated again, thistime in a second zone located above the plug. A ball then is deployedonto the plug. The ball will restrict fluids from flowing through andpast the plug. When fluids are injected into the liner, therefore, theywill be forced to flow out the perforations and into the second zone.After the second zone is fractured, the process is repeated until allzones in the well are fractured.

After the well has been fractured, however, plugs may interfere withinstallation of production equipment in the liner or may restrict theflow of production fluids upward through the liner. Thus, the plugstypically are removed from the liner after the well has been fractured.Retrievable plugs are designed to be set and then unset. Once unset,they may be removed from the well. Non-retrievable plugs are designed tobe more or less permanently installed in the liner. Once installed, theymust be drilled out to open up the liner. Moreover, the debris createdby drilling out non-retrievable plugs must be circulated out of the wellso it does not interfere with production equipment that will beinstalled in the liner.

Many conventional non-retrievable plugs have a common basic design builtaround a central support mandrel. The support mandrel is generallycylindrical and somewhat elongated. It has a central conduit extendingaxially through it. The support mandrel serves as a core for the plugand provides support for the other plug components. The other plugcomponents—slips, wedges, and sealing elements—are all generally annularand are carried on and around the support mandrel in an array extendingalong the length of the mandrel.

More particularly, an upper set of slips is carried on the supportmandrel adjacent to an upper wedge (also referred to as a “cone”). Alower set of slips is disposed adjacent to a lower wedge. The slips andwedges have mating, ramped surfaces. An annular sealing element, usuallyan elastomeric sealing element, is carried on the support mandrelbetween the upper and lower wedges. The sealing element often isprovided with backup rings. The various components are carried on thesupport mandrel such that they may slide along the mandrel.

Such conventional frac plugs have nominal outer diameters in their“unset” position that allow them to be deployed into a liner. Oncedeployed, they will be set by radially expanding the slips and sealingelement into contact with the liner walls. More specifically, the plugsare installed with a setting tool which may be actuated to applyopposing axial forces to the components carried around the plug supportmandrel. The axial forces cause the components to slide axially alongthe support mandrel and squeeze together. As they are squeezed together,the ramped surfaces on the inside of the slips will cause the slips toride up the ramped outer surface of the wedges. As they ride up theouter surface of the wedges, the slips expand radially until theycontact the inner wall of the liner. The outer surfaces of the slipshave teeth, serrations, and the like that enable the slips to jam andbite into the liner wall. The slips, therefore, provide the primaryanchor which holds the plug in place.

Squeezing the components also will cause the elastomeric sealing elementto expand radially until it seals against the liner wall. Backup rings,if present, serve to minimize axial extrusion of the elastomericmaterial as it is squeezed between the upper and lower wedges. Theelastomeric sealing element thus can minimize or eliminate flow aroundthe plug, i.e., between the plug and the liner wall.

The support mandrel has a ball seat at or very near the upper end of themandrel central conduit. Once the plug is installed, and the settingtool withdrawn, fluids can flow in both directions through the centralconduit. A ball may be deployed or “dropped” onto the ball seat,however, to substantially isolate the portions of the liner below theplug. The ball will restrict fluid from flowing downward through theplug.

Such designs are well known in the art and variations thereof aredisclosed, for example, in U.S. Pat. No. 7,475,736 to a Lehr et al.,U.S. Pat. No. 7,789,137 to R. Turley et al., U.S. Pat. No. 8,047,280 toL. Tran et al., and U.S. Pat. No. 9,316,086 to D. VanLue. Plugs of thatgeneral design also are commercially available, such as Schlumberger'sDiamondback composite drillable frac plug and Weatherford's TniFraccomposite frac plug.

Frac plugs must resist very high hydraulic pressure—often as high as15,000 psi or more. They also may be exposed to elevated temperaturesand corrosive liquids. Thus, frac plugs traditionally were composed ofrelatively durable materials such as steel. Frac plugs fabricated withmetal components have greater structural strength that may in turnfacilitate installation of the plug. Metal components also may be lesslikely to loosen up and become unset, and they are more resistant tocorrosion. On the other hand, the required service life of frac plugsmay be relatively short, and metallic plugs are difficult to drill out.

Thus, some or all of the components of many conventional non-retrievablefrac plugs now are fabricated from more easily drillable materials. Suchmaterials include cast iron, aluminum, and other more brittle or softermetals. Other more easily drillable materials include fiberglass, carbonfiber materials, and other composite materials. Composite materials inparticular are more easily drilled and, therefore, can make it easier todrill out a plug. They also can allow for less aggressive drilling andreduce the likelihood and amount of resulting damage to a liner.

It will be appreciated, however, that the central conduit of manyconventional composite plugs has a relatively small diameter. Smallerdiameter bores make it more likely that the plug will significantlyrestrict the flow of production fluids through the plug, or that it willnot accommodate the passage of other tools that may be needed forremedial operations. Thus, there is a greater likelihood with small-boreplugs that the plugs will have to be drilled out.

Even with composite plugs, drill out operations can be costly and timeconsuming. Coil tubing drill outs typically cost $100,000.00 per day,and the process may take two to three days. Moreover, a plug and perffrac job may require the installation of dozens of plugs. Thus, even asmall increase in the time required to drill an individual plug mayconsiderably lengthen the overall cost and time required for theoperation.

It also will be appreciated that composite materials lack the hardnessand strength of metals such as steel, cast iron, and aluminum. Plugsfabricated from composite materials may not hold their set or seal. Theymay be dislodged, damaged, or leak during the fracturing process ascomposite materials generally lack the yield strength of metals.Composites also have much lower lateral shear strengths, and thus, aremore susceptible to being blown out by a ball once hydraulic pressureabove the ball is increased. Such deficiencies often are minimized byincreasing the length and thickness of the plug components.

For example, making a support mandrel thicker will increase its radialyield strength and will help maintain the engagement of the slips with aliner wall. A longer support mandrel will have a proportionately higherlateral shear strength and, therefore, is better able to resist theforce of a ball seated in the mandrel passageway. Increasing the size ofthe components, however, necessarily increases the time required todrill the plug and increased the amount of debris that must becirculated out of the well.

Additionally, while many of their components are fabricated fromcomposites, many so-called composite plugs may still incorporate metalcomponents which can slow down or complicate drilling out of the plug.For example, many predominantly composite plugs incorporate metallicslips which increase the time required to drill out the plug. Metalslips also can break up into relatively large pieces that may be moredifficult to circulate out of a well.

Also, as noted, the elastomeric sealing element in many conventionalplugs is disposed initially between the upper and lower wedges. As thewedges are squeezed together, the elastomeric sealing element isexpanded radially. There also will be a tendency, however, for theelastomeric materials to extrude axially over and around the surface ofthe wedges. When hydraulic pressure later is applied behind the plug, italso to may tend to extrude the elastomeric seal. Thus, many compositeplugs incorporate metal or composite rings to back up the elastomericseal. Such backup rings are not always effective in preventingextrusion. Metal rings especially can become entangled around the bitused to drill the plug.

The process of drilling out plugs also can be exacerbated by what isreferred to as “spinning.” That is, as a plug is drilled out, theportions of the plug components remaining after most of the plug hasbeen drilled out tend to spin with the bit. Given their relatively lowermechanical properties, spinning is a particular problem in compositeplugs and can significantly increase the time required to drill out aplugs. A common solution is to provide interlocking mechanical featureson the top and bottom of the plugs. Thus, if the remnant of a plugbegins to spin with a bit, it will be pushed down by the bit until itslower end interlocks with the top of a plug installed lower down in theliner. That interlocking engagement will stop the plug remnant fromspinning. Such interlocking geometrical features, however, can addlength and material to the plug.

Finally, as various problems attendant to their installation anddrilling out have been addressed, composite plugs have tended to becomerelatively complex. Composite materials in general can be relativelyexpensive, and adding to the complexity and number of components in aplug generally tends to increase the cost of fabricating and assemblingthe plug. Typical plug and perf jobs will require dozens of plugs, soeven small increases in the cost of a plug can add up to a significantexpense.

The statements in this section are intended to provide backgroundinformation related to the invention disclosed and claimed herein. Suchinformation may or may not constitute prior art. It will be appreciatedfrom the foregoing, however, that there remains a need for new andimproved composite plugs and for new and improved methods for frackingor otherwise stimulating formations using composite plugs. Suchdisadvantages and others inherent in the prior art are addressed byvarious aspects and embodiments of the subject invention.

SUMMARY OF THE INVENTION

The subject invention relates generally to plugs that may be used toisolate a portion of a well and encompasses various embodiments andaspects, some of which are specifically described and illustratedherein.

In one embodiment, a plug apparatus includes an annular wedge having awedge first end and a wedge second end. The wedge includes an axialwedge passage therethrough from the wedge first end to the wedge secondend. The wedge includes an inner seat defined in the wedge passage forreceiving and seating a ball. The wedge has a tapered outer surfaceadjacent the wedge second end. The tapered outer surface increases inoutside diameter from the wedge second end toward but not necessarilyall the way to the wedge first end. A sealing ring is received about thetapered outer surface of the wedge. The sealing ring is radiallyexpandable. An annular slip has a slip first end and a slip second end.The slip has an axial slip passage therethrough from the slip first endto the slip second end. The slip passage has a tapered inner surfaceadjacent the slip first end. The tapered inner surface decreases ininside diameter from the slip first end toward but not necessarily allthe way to the slip second end. The wedge second end is received in theslip first end so that the tapered outer surface of the wedge engagesthe tapered inner surface of the slip. The slip first end faces thesealing ring for abutment with the sealing ring.

The annular slip can include a plurality of separate slip segments. Theannular wedge can also include a plurality of collet fingers extendingfrom the wedge second end and circumferentially spaced to form slotsbetween the collet fingers, each collet finger extending through theaxial slip passage to a distal end beyond the slip second end. The plugapparatus can further include a setting ring having an outer diameter,slidably mounted around the collet fingers between the slip second endand the distal end of each collet finger. The setting ring can have afirst radial thickness and one or more keys that protrude radiallyinward into one or more of the slots from the first radial thickness toa second radial thickness. The plug apparatus can further include agauge ring fixably connected to the distal end of the collet fingershaving an outer diameter at least the same as the outer diameter of thesetting ring or greater. As an alternative option, the setting ring canbe located adjacent to the gauge ring and to the slip second end, andthe gauge ring can include a peripheral annular wall that extends aroundthe setting ring and extends at least to the slip second end.

According to one aspect, the setting ring is slidable between an unsetposition and a set position. In the unset position, the slip and thesealing ring are each in a first radial position wherein the settingring is located adjacent to the gauge ring and to the slip second end.In the set position, the slip and the sealing ring are each radiallyexpanded from the first radial position to a second radial position,wherein the setting ring is displaced along the collet fingers towardsthe wedge second end and the adjacent slip and sealing ring arecorrespondingly displaced towards the wedge first end.

The plug apparatus can yet further include a mandrel connected to asetting tool, the mandrel extending through the axial wedge passage andreleasably coupled to the setting ring via a frangible coupling. Theplug apparatus can still further include an annular sleeve adapterconnected to the setting tool and coupled to the first wedge end of theannular wedge, wherein the setting tool is configured to displace themandrel axially relative to the annular sleeve adapter and thereby movethe setting ring from the unset position to the set position.

In an alternative embodiment, a plug apparatus comprises an annular slipformed from a plurality of separate slip segments disposed adjacently toone another. The slip has an upper end and a lower end, and a slip borethat extends from the slip's upper end to its lower end and is alsoinwardly tapered from the upper end toward the lower end. The plugapparatus further comprises a wedge with a tapered lower outer surfaceportion that is received in the upper end of the slip and engages thetapered slip bore. The wedge includes a wedge bore with an upwardlyfacing annular seat defined therein. A plurality of collet fingers,circumferentially spaced in an annular arrangement, extends axially froma lower end of the tapered lower outer surface portion of the wedge.Each collet finger extends through the slip bore to a distal end beyondthe slip lower end. A setting ring is slidably located on the pluralityof collet fingers between the slip lower end and the distal end of thecollet fingers. The plug apparatus yet further comprises a sealing ringreceived about the tapered lower outer surface portion of the wedgeabove the slip upper end and is configured to be engaged by the slipupper end.

A method is disclosed for setting a plug in a casing bore, the methodcomprising initially retaining a wedge and a slip in an unset axiallyextended position with a lower tapered outer surface of the wedgereceived in an upper tapered inner bore of the slip. A sealing ring isreceived about the wedge above the slip and engaged with an upper end ofthe slip. While the wedge and the slip are retained in the unsetposition, the plug is run into a casing to a casing location to beplugged. The plug then is set in the casing by forcing the wedge axiallyinto the slip and the sealing ring; thereby radially expanding the slipto anchor the plug in the casing, and radially expanding the sealingring to seal between the plug and the casing.

In another embodiment, an adapter apparatus is provided for attaching aplug onto a downhole setting tool. The setting tool including an innersetting tool part and an outer setting tool part. The setting tool isconfigured to provide a relative longitudinal motion between the innerand outer setting tool parts. The adapter apparatus includes an outeradapter portion configured to be attached to the outer setting toolpart, the outer adapter portion including downward facing settingsurface. The adapter apparatus further includes an inner adapter portionconfigured to be attached to the inner setting tool part, the inneradapter portion including an inner mandrel, a release sleeve, and areleasable connector. The release sleeve is slidably received on theinner mandrel, the release sleeve carrying an upward facing settingsurface. The releasable connector is configured to hold the releasesleeve in an initial position relative to the inner mandrel until acompressive force transmitted between the downward facing settingsurface and the upward facing setting surface exceeds a predeterminedrelease value.

In another embodiment, an adapter apparatus is provided for attaching aplug onto a downhole setting tool. The setting tool including an innersetting tool part and an outer setting tool part. The setting tool isconfigured to provide a relative longitudinal motion between the innerand outer setting tool parts. The adapter apparatus includes an outeradapter portion configured to be attached to the outer setting toolpart, the outer adapter portion including downward facing settingsurface. The adapter apparatus further includes an inner adapter portionconfigured to be attached to the inner setting tool part, the inneradapter portion including an inner mandrel, a release sleeve, and areleasable connector. The release sleeve is slidably received on theinner mandrel, the release sleeve carrying an upward facing settingsurface. The releasable connector is configured to hold the releasesleeve in an initial position relative to the inner mandrel until acompressive force transmitted between the downward facing settingsurface and the upward facing setting surface exceeds a predeterminedrelease value.

A method is provided for setting a plug assembly in a casing bore. Themethod comprises connecting the plug assembly in an initial arrangementwith a setting tool using an adapter kit. The initial arrangementincludes the plug assembly including a plug wedge in an initial positionpartially received in a plug slip, with a sealing ring received aroundthe plug wedge adjacent an end of the slip. The plug wedge and plug slipare received about an inner part of the adapter kit, with an upwardfacing setting surface of the inner part facing a lower end of the plugassembly. An outer part of the adapter kit including a downward facingsetting surface facing an upper end of the plug assembly. The plugassembly, the adapter kit, and the setting tool is run into the casingbore in the initial arrangement. The plug assembly is set in the casingbore by actuating the setting tool and compressing the plug assemblybetween the upward facing and downward facing setting surfaces. The plugassembly is released from the adapter kit.

The subject invention provides other embodiments and aspects, includinga plug apparatus, comprising a wedge, a sealing ring, and a slip. Thewedge comprises an axial wedge bore. A seat is defined in the wedgebore. The seat is adapted to receive a ball. The wedge also has atapered outer surface. The tapered outer surface decreases in diameterfrom the upper extent of the tapered outer surface toward the lowerextent of the tapered outer surface. The sealing ring is received aroundthe tapered outer surface of the wedge. The sealing ring has an axialring bore and is radially expandable. The slip comprises an axial slipbore. The slip bore provides the slip with a tapered inner surface. Thetapered inner surface decreases in diameter from the upper extent of thetapered inner surface toward the lower extent of the tapered innersurface. The inner surface is adapted to receive the wedge along thetapered outer surface of the wedge. The wedge is adapted fordisplacement from an unset position generally above the slip to a setposition wherein the wedge is received in the slip bore along thetapered outer surface of the wedge.

Other embodiments include such plug apparatus where the sealing ring andthe slip are adapted to expand radially from an unset condition. In theunset position the sealing ring and the slip have nominal outerdiameters. The slip expands radially from its unset condition to a setcondition as the wedge is displaced from its unset position to its setposition. In its set condition, the sealing ring and the slip haveenlarged outer diameters.

Additional aspects are directed to such plug assemblies where a lowerportion of the tapered outer surface of the wedge, when the wedge is inits unset position, extends into and engages an upper portion of thetapered inner surface of the slip.

Still other embodiments are directed to such plug assemblies where thesealing ring includes an annular ring body. The annular ring body has atapered ring bore complementary to the tapered outer surface of thewedge. An annular inner groove is defined in the ring bore. An annularouter groove is defined in the outer surface of the ring body. An innerelastomeric seal is received in the inner groove. An outer elastomericseal is received in the outer groove.

Further aspects and embodiments are directed to such plug assemblieswhere the slip comprises a plurality of separate slip segments. Yetothers are direct to such plug assemblies where the sealing ring isradially expandable without breaking and where the sealing ring includesan annular ring body constructed of a sufficiently ductile material suchthat the sealing ring can expand radially to its set condition withoutbreaking.

The subject invention also is directed to embodiments where such plugassemblies have a sealing ring fabricated from plastic and especiallyfrom engineering plastics. In other embodiments the plastic is selectedfrom plastics or engineering plastics selected from the group consistingof polycarbonates, polyamides, polyether ether ketones, andpolyetherimides and copolymers and mixtures thereof or the groupsconsisting of subsets of such groups.

In other aspects and embodiments the sealing ring is fabricated fromplastic and has a elongation factor of at least about 10% or at leastabout 30%. In other aspects, the plastic will have a useful operatingtemperature of at least 250° F. or at least 350° F., or will have atensile strength of a least 5,000 psi or at least about 1,500 psi.

Still other embodiments include such plug apparatus where the ball seatis located in the wedge bore such that when the wedge is in its setposition the ball seat is situated axially proximate to the sealingring, or where the ball seat is located in the wedge bore axially belowthe upper end of the wedge bore, or where the ball seat is located inthe wedge bore such that when the wedge is in its set position the ballseat is situated axially between the upper end of the sealing ring andthe lower end of the slip, or where the ball seat is located in thewedge bore such that when the wedge is in its set position the ball seatis situated axially below the midpoint of the slip bore.

Additional aspects are directed to such plug assemblies where the ballseat is to provided by an upward facing tapered reduction in thediameter of the wedge bore or where the tapered reduction in diameter isapproximately 15° off center.

In other embodiments, such plug apparatus have wedges where the taperedouter surface of the wedge is a truncated, inverted cone and the taperedinner surface of the slip is a truncated, inverted cone. In otheraspects, the tapered outer surface of the wedge and the tapered innersurface of the slip are provided with a taper from about 1° to about 10°off center or where the tapered outer surface of the wedge and thetapered inner surface of the slip provide a self-locking taper fitbetween the wedge and the slip.

Other embodiments of the invention are directed to such plug apparatuswhere the slip comprises a plurality of separate slip segments. Each ofthe slip segments are configured generally as lateral segments of anopen cylinder. In other aspects, the slip segments are aligned axially.When the wedge is in its unset position, the slip segmentscircumferentially abut along their sides and provide a substantiallycontinuous inner tapered surface of the slip. In still other aspects theupper end of the slip abuts the sealing ring about the lower end of thesealing ring as the wedge moves from its unset position to its setposition. In other embodiments, the upper end of the slip, when thewedge is in its unset position, abuts the sealing ring substantiallycontinuously about the lower end of the sealing ring.

Other embodiments and aspects of the invention are directed to plugapparatus comprising a wedge, a plastic sealing ring, and a slip. Thewedge comprises an axial wedge bore and a tapered outer surface. Thetapered outer surface decreases in diameter from the upper extent of thetapered outer surface toward the lower extent of the tapered outersurface. The plastic sealing ring is received around the tapered outersurface of the wedge. The sealing ring has an axial ring bore and isradially expandable. The slip comprises an axial slip bore. The slipbore provides the slip with a tapered inner surface. The tapered innersurface decreases in diameter from the upper extent of the tapered innersurface toward the lower extent of the tapered inner surface. The innersurface is adapted to receive the wedge along the tapered outer surfaceof the wedge. The wedge is adapted for displacement from an unsetposition generally above the slip to a set position wherein the wedge isreceived in the slip bore along the tapered outer surface of the wedge.Displacement of the wedge is adapted to radially expand the sealing ringinto sealing engagement with a liner without breaking the sealing ring.

Additional aspects and embodiments are directed to such plug apparatuswhere the comprises a plurality of collet fingers. The collet fingersextend axially below the tapered outer surface of the wedge. They arecircumferentially spaced to form axial slots between the collet fingers.They also extend through the slip bore to a distal end beyond the slipwhen the wedge is in the unset position.

In other embodiments, such plug apparatus have a setting ring slidablymounted around the collet fingers between the slip and the distal end ofthe collet fingers. The setting ring has an outer diameter, a firstradial thickness; and one or more keys that protrude radially inwardfrom the first radial thickness to a second radial thickness and intoone or more of the slots between the collet fingers.

Further embodiments are directed to such plug apparatus having a gaugering connected to the distal end of the collet fingers and having anouter diameter equal to or greater than the outer diameter of thesetting ring. In other embodiments, the setting ring is between the slipand a lower portion of the gauge ring and the gauge ring includes aperipheral annular wall that extends axially upward around the settingring and at least of portion of the slip.

Yet other embodiments are directed to plug apparatus where the wedge isadapted for displacement from the unset position to the set position. Inthe unset position the slip and the sealing ring are each in a firstradial position and the setting ring is located adjacent to the gaugering and to the slip. In the set position, the slip and the sealing ringare each radially expanded from the first radial position to a secondradial position and the setting ring is located adjacent to the slip andthe distal ends of the collet fingers are displaced away from thesetting ring.

Additional aspects and embodiments are directed to such plug apparatuswhich have a mandrel and a sleeve adapter. The mandrel is operablyconnected to a setting tool and extends through the wedge bore andreleasably coupled to the setting ring by a frangible coupling. Thesleeve adapter is operably connected to the setting tool and abuts theupper end of the wedge. The setting tool is configured to displace thesleeve adapter axially downward relative to the mandrel and therebydisplace the wedge from the unset position to the set position.

In other aspects, the invention is directed to such plug assemblies as acomposed of drillable materials, including composite materials, andespecially where the wedge and slip are fabricated from such materials.

The subject invention in other aspects and embodiments also provides formethods of setting a plug in a liner bore. The methods comprise runningthe plug into the liner to a location to be plugged. The plug is in anunset state in which a tapered outer surface of a wedge is generallyabove a tapered inner bore of a slip. A sealing ring is received aroundthe tapered outer surface of the wedge above the slip. The plug then isset in the liner by forcing the wedge axially into the slip bore and thesealing ring. Thus, the slip will be radially expanded to anchor theplug in the liner, and the sealing ring will be radially expanded toseal between the plug and the liner.

Other aspects provide such methods where the sealing ring expandsradially without breaking. In other embodiments, the slip abuts thesealing ring as the wedge is forced into the slip bore and sealing ring.In yet other embodiments the slip, when the plug is in its unset state,abuts the sealing ring substantially continuously about the sealingring. Other embodiments include deploying a ball onto an annular seatdefined in an axial bore of the wedge to occlude the axial bore.

Still other aspects of the invention are directed to liner assemblieswhich comprise a liner with the novel plug assemblies set therein and tooil and gas wells incorporating such liner assemblies.

Finally, still other aspect and embodiments of the novel apparatus andmethods will have various combinations of such features as will beapparent to workers in the art.

Thus, the present invention in its various aspects and embodimentscomprises a combination of features and characteristics that aredirected to overcoming various shortcomings of the prior art. Thevarious features and characteristics described above, as well as otherfeatures and characteristics, will be readily apparent to those skilledin the art upon reading the following detailed description of thepreferred embodiments and by reference to the appended drawings.

Since the description and drawings that follow are directed toparticular embodiments, however, they shall not be understood aslimiting the scope of the invention. They are included to provide abetter understanding of the invention and the manner in which it may bepracticed. The subject invention encompasses other embodimentsconsistent with the claims set forth herein.

BRIEF DESCRIPTION OF TILE DRAWINGS

FIG. 1A is a schematic illustration of an early stage of a “plug andpert” fracturing operation showing a tool string 10 deployed into aliner assembly 4, where tool string 10 includes a perf gun 11, a settingtool 12, an adapter kit 14, and a first preferred embodiment 16 of theplug assemblies of the subject invention.

FIG. 1B is a schematic illustration of liner assembly 4 after completionof the plug and perf fracturing operation, but before removal of plugs16 from liner 4.

FIGS. 2-4 are sequential axial cross-sectional schematic views of plug16 in a well liner 4 which omit, for the sake of clarity, variouscomponents of adapter kit 14.

FIG. 2 shows plug 16 in its run-in state, that is, as it is run into awell to a desired location in liner 4.

FIG. 3 shows plug 16 after it has been installed in liner 4.

FIG. 4 shows plug 16 after it has been closed with a ball 76 to restrictthe flow of fluids downward through plug 16.

FIG. 5 is an enlarged axial cross-sectional view of an annular wedge 62of plug 16.

FIG. 6 is an enlarged axial cross-sectional view of a sealing ring 64 ofplug 16.

FIG. 7 is an enlarged axial cross-sectional view of an annular slip 66of plug 16.

FIG. 8 is bottom elevational view of slip 66 of plug 16.

FIGS. 9A and 9B are axial cross-sectional views of a portion of a toolstring 10 which includes setting tool 12, adapter kit 14 and plug 16.Setting tool 12, adapter kit 14, and plug 16 are shown as they are runinto a well. FIG. 9A shows an upper portion of tool string 10, and FIG.9B shows a lower portion of tool string 10.

FIG. 10 is an enlarged cross-sectional view of a lower portion ofsetting tool 12, adapter kit 14, and plug 16 shown in FIGS. 9A-9B.

FIG. 11 is an enlarged axial cross-sectional view of adapter kit 14 andplug 16 shown in FIGS. 9B and 10. Adapter kit 14 and plug 16 are intheir unactuated, run-in state.

FIG. 12 is a still further enlarged axial cross-sectional view of plug16 and various components of adapter kit 14.

FIGS. 13-16 are sequential axial cross-sectional views of adapter kit 14and plug 16 which, together with FIGS. 11-12, illustrate the operationof setting tool 12 and adapter kit 14 as they are deployed into a wellwith plug 16, are actuated to install plug 16 in liner 4, and then arereleased from plug 16.

FIG. 13 shows adapter kit 14 and plug 16 after they have been actuatedfrom their run-in state shown in FIG. 11 to install plug 16 in liner 4.

FIG. 14 shows an initial stage of releasing and withdrawing adapter kit14 from set plug 16.

FIG. 15 shows an intermediate stage of releasing and withdrawing adapterkit 14 from set plug 16.

FIG. 16 shows a later stage of releasing and withdrawing adapter kit 14.

FIG. 17 is an axial cross-sectional view of the lower end of adapter kit14 and plug 16 shown in FIG. 12 with an optional pump down fin 144connected to adapter kit 14.

FIG. 18 is a perspective view of a tension mandrel lock spring 150 usedin connecting certain components of adapter kit 14.

FIG. 19 is an enlarged axial cross-sectional view of a second preferredembodiment 216 of plug assemblies of the subject invention. Plug 216 isshown in its run-in state, and the figure omits for the sake of claritycertain components of an adapter kit 214.

FIG. 20 is side elevational view, including a partial cut-away axialcross-section, of plug 216. Plug 216 is shown in its run-in state, andthe figure omits for the sake of clarity certain components of adapterkit 214.

FIG. 21 is an axial cross-sectional view of an annular wedge 262 of plug216.

FIG. 22 is a radial cross-section view, taken generally along lines22-22 of FIG. 19, of plug 216.

FIGS. 23 and 24 are sequential axial cross-sectional views of plug 216in liner 4 omitting, for the sake of clarity, various components ofadapter kit 214.

FIG. 23 shows plug 216 in an unset position as it is run into a well toa desired location in liner 4.

FIG. 24 shows plug 216 after it has been set in liner 4 and it has beenclosed with a ball 76 to restrict the flow of fluids downward throughplug 216.

FIG. 25 is a top elevational view of a setting ring 270 of plug 216.

FIG. 26 is an axial cross-sectional view of setting ring 270 shown inFIG. 25.

FIG. 27 is an axial cross-sectional view of a gauge ring 280 of plug216.

FIG. 28 is a bottom elevational view of gauge ring 280 shown in FIG. 27.

FIG. 29 is an axial cross-sectional view, similar to the view of FIG.12, showing portions of setting tool 12 and adapter kit 214 with plug216. Setting tool 12, adapter kit 214, and plug 216 are in theirunactuated, run-in state.

FIG. 30 is an enlarged axial cross-sectional view of adapter kit 214 andplug 216 shown in FIG. 29.

FIG. 31 is an axial cross-sectional view of an actuating mandrel 222 ofadapter kit 214.

FIG. 32 is an axial cross-sectional view of a top cap 224 of adapter kit214.

FIG. 33 is an axial cross-sectional view of a sleeve adapter 210 ofadapter kit 214.

In the drawings and description that follows, like parts are identifiedby the same reference numerals. The drawing figures are not necessarilyto scale. Certain features of the embodiments may be shown exaggeratedin scale or in somewhat schematic form and some details of conventionaldesign and construction may not be shown in the interest of clarity andconciseness.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention generally relates to plugs that may be used toisolate a portion of a well, and more particularly, to plugs that may beused in fracturing or other processes which require isolation ofselected portions of a liner. Some broader embodiments of the novelplugs comprise an annular wedge having an inner ball seat, a sealingring, and an annular slip. Other broad embodiments comprise an annularwedge, a plastic sealing ring which can expand radially withoutbreaking, and an annular slip.

Overview of Plug and Perf Fracturing Operations

A first preferred frac plug 16, for example, will be described byreference to FIGS. 1-18. As may be seen in the schematic representationsof FIG. 1, plugs 16 may be used to perform a “plug and perf” fracturingoperation in an oil and gas well 1. Well 1 is serviced by a well head 2and various other surface equipment (not shown). Well head 2 and theother surface equipment will allow frac fluids to be introduced into thewell at high pressures and flow rates. The upper portion of well 1 isprovided with a casing 3 which extends to the surface. A productionliner 4 has been installed in the lower portion of casing 3 via a linerhanger 5. It will be noted that the lower part of well 1 extendsgenerally horizontally through a hydrocarbon bearing formation 6 andthat liner 2, as installed in well 1, is not provided with valves or anyopenings in the walls thereof. Liner 2 also has been cemented in place.That is, cement 7 has been introduced into the annular space betweenliner 2 and the well bore 8.

FIG. 1A shows well 1 after the initial stage of a frac job has beencompleted. As discussed in greater detail below, a typical frac job willproceed from the lowermost zone in a well to the uppermost zone. FIG.1A, therefore, shows that the bottom portion of liner 4 has beenperforated and that fractures 9 extending from perforations 13 a havebeen created in a first zone near the bottom of well 1. Tool string 10has been run into liner 4 on a wireline 15.

Tool string 10 comprises a pelf gun 11, setting tool 12, adapter kit 14,and frac plug 16 a. Tool string 10 is positioned in liner 4 such thatfrac plug 16 a is uphole from perforations 13 a. Frac plug 16 a iscoupled to setting tool 12 by adapter kit 14 and, as discussed ingreater detail below, will be installed in liner 4 by actuating settingtool 12.

Once plug 16 a has been installed, setting tool 12 and adapter kit 14will be released from plug 16 a. Perf gun 11 then will be fired tocreate perforations 13 b in liner 4 uphole from plug 16 a. Perf gun 11,setting tool 12, and adapter kit 14 then will be pulled out of well 1 bywireline 15.

A frac ball (not shown) then will be deployed onto plug 16 a to restrictthe downward flow of fluids through plug 16 a. Plug 16 a, therefore,will substantially isolate the lower portion of well 1 and the firstfractures 9 extending from perforations 13 a. Fluid then can be pumpedinto liner 4 and forced out through perforations 13 b to createfractures 9 in a second zone.

Additional plugs 16 b to 16 y then will be run into well 1 and set,liner 4 will be perforated at perforations 13 c to 13 z, and well 1 willbe fractured in succession as described above until, as shown in FIG.1B, all stages of the frac job have been completed and fractures 9 havebeen established in all zones.

Some operators may prefer to produce hydrocarbons from well 1 withoutremoving plugs 16 from liner 4. In such instances, dissolvable fracballs will be used in the fracturing operation. Dissolvable balls, astheir name implies, are fabricated from a material that dissolves,softens, or disintegrates in the presence of well fluids after a periodof time (typically 1 to 30 days) such that the balls do not thereafterinterfere with the upward flow of fluids through plugs 16.

More commonly, however, operators will prefer to remove plugs 16 fromliner 4, even if dissolvable frac balls are employed. Frac plugs 16 mayinterfere with the installation of production equipment in liner 4 and,depending on production rates, may restrict the upward flow ofproduction fluids through liner 4. Thus, for example, a motor with adrill bit may be deployed into liner 4 on coiled tubing. Mill bits alsomay be used but generally are less preferable. In either event, plugs 16will be drilled out in succession from top to bottom. The drillingprocess, of course, creates debris which, if left in liner 4, mayinterfere with production equipment or otherwise may hinder productionfrom well 1. Debris from plugs 16, therefore, preferably is circulatedout of liner 4 during the drilling process.

It will be noted that FIG. 1 are greatly simplified schematicrepresentations of a plug and pert fracturing operation. Productionliner 4 is shown only in part as such liners may extend for asubstantial distance. The portion of liner 4 not shown also will beprovided with perforations 13 and plugs 16, and fractures 9 will beestablished therein. In addition, FIG. 1 depict only a few perforations13 in each zone, whereas typically a zone will be provided with manyperforations. Likewise, a well may be fractured in any number of zones,thus liner 4 may be provided with more or fewer plugs 16 than depicted.

The terms “upper” and “lower” as used herein to describe location ororientation are relative to the well and to the tool as run into andinstalled in the well. Thus, “upper” refers to a location or orientationtoward the upper or surface end of the well. “Lower” is relative to thelower end or bottom of the well. It also will be appreciated that thecourse of the well bore may not necessarily be as depicted schematicallyin FIG. 1. Depending on the location and orientation of the hydrocarbonbearing formation to be accessed, the course of the well bore may bemore or less deviated in any number of ways. “Axial,” “radial,” andforms thereof reference the central axis of the tool. For example, axialmovement or position refers to movement or position generally along orparallel to the central axis. “Lateral” movement and the like generallyrefers to up and down movement or position up and down the tool.

Overview of First Preferred Frac Plug

The novel plugs incorporate a wedge, a sealing ring, and a slip, all ofwhich have truncated inverted conical or other tapered surfaces. Thetapered surfaces complement each other and allow the wedge to be driveninto and radially expand the sealing ring and slip to seal and anchorthe plug in a liner. For example, consider preferred novel frac plug 16which is shown in isolation and in greater detail in FIGS. 2-4. As showntherein, plug 16 generally comprises an annular wedge 62, a sealing ring64, and an annular slip 66. The construction of those plug componentsperhaps can be best appreciated from FIGS. 5-8. Annular wedge 62 isshown in isolation in FIG. 5, sealing ring 64 is shown in isolation inFIG. 6, and annular slip 66 is shown in isolation in FIGS. 7 and 8. Allof those figures show plug 16 and its components in their as-fabricated,run-in state.

As best seen in FIG. 5, wedge 62 may be described in general terms ashaving a generally tapered annular or open cylindrical shape. Moreparticularly, wedge 62 has an axial passage or bore 72 extending fromthe upper end 68 of wedge 62 to the lower end 70 of wedge 68. An innerball seat 74 is defined in wedge bore 72, bore 72 otherwise having asubstantially uniform diameter. Ball seat 74 is provided by a shallowangle, upward facing tapered reduction in the diameter of wedge bore 72situated axially below the upper end 68 of wedge 62.

The outer surface of wedge 62 in large part tapers radially outward frombottom to top. More specifically, the outer diameter of wedge 62increases from the wedge lower end 70 toward the wedge upper end 68,thus providing wedge 62 with an inverted truncated conical outer surface78 adjacent to the wedge lower end 70. Tapered outer surface 78 extendsalong the majority of the length of wedge 62 and terminates near itsupper end 68. Though perhaps not readily apparent in FIG. 5, arelatively short upper portion 80 of wedge 62 has a substantiallyuniform, non-tapered outer diameter.

As seen best in FIG. 6, sealing ring 64 has a relatively short, annularbody 82 defining an axial passage or bore 84. Ring bore 84 has agenerally inverted truncated conical shape, that is, it tapers radiallyoutward from its lower end to its upper end. The taper of ring bore 84is complementary to the tapered outer surface 78 of wedge 62. Sealingring 64 preferably is provided with elastomeric seals which ultimatelywill enhance the seal between plug 16 and liner 4 when, as described indetail below, plug 16 is set. Thus, as appreciated best from FIG. 6,ring body 82 has an annular groove 86 in its outer surface 88 and anannular groove 90 in its ring bore 84. Outer groove 86 and inner groove90 are filled, respectively, with elastomeric seal material 92 and 94.Elastomeric seal material 92 and 94 may be molded in grooves 86 and 90or they may be molded and then inserted therein.

As best seen in FIGS. 7-8, slip 66 also may be described in generalterms as having a generally tapered annular or open cylindrical shape.More particularly, slip 66 has an axial passage or bore 100 extendingfrom the upper end 96 of slip 66 to the lower end 98 of slip 66. Slipbore 100 in large part has a generally inverted truncated conical shape,that is, it in large part tapers radially inward from top to bottom.More specifically, the inner diameter of slip bore 100 decreases fromthe slip upper end 96 toward the slip lower end 98, thus providing slip66 with a tapered inner surface 102 adjacent the slip upper end 96.Tapered inner surface 102 extends along most of slip bore 100 andterminates near the lower end 98 of slip 66. The taper of inner surface102 of slip 66 is complementary to the taper of outer surface 78 ofwedge 62. Though perhaps not readily apparent in FIG. 7, a relativelyshort lower portion 104 of slip bore 100 has a substantially uniform,non-tapered inner diameter.

Slip 66 is a breakaway type slip which is designed to break apart into anumber of segments. More particularly, slip 66 has a plurality of slipsegments 112, such as slip segments 112A, 112B, and 112C. Slip segments112 are joined initially by frangible portions 114. Slip segments 112are arranged around the circumference of slip 66 and extend laterally(or lengthwise) from the slip upper end 96 to the slip lower end 98.Longitudinal cuts separate the upper portion of adjacent slip segments112 and align with grooves 116 in the outer surface of slip 66. Whenplug 16 is set, as described in detail below, the longitudinal cuts andgrooves 116 encourage slip segments 112 to break apart at frangibleportions 114. Alternately, however, slip 66 may be assembled fromdiscrete slip segments. In any event, the substantial length of theouter surface of slip segments 112 is covered with downward facingserrations or teeth which will allow slip segments 112 to engage andgrip liner 4.

As described in greater detail below, wedge 62 will be driven downwardinto sealing ring 64 and annular slip 66. As wedge 62 is drivendownward, it will force sealing ring 64 and slip 66 to expand andthereby set and seal plug 16 in liner 4. The operation of plug 16perhaps can be best appreciated from FIGS. 2-4 which show plug 16,respectively, as it is run into well 1 and positioned in liner 4, afterit has been set in liner 4, and with a frac ball 76 seated in plug 16 toisolate lower portions of liner 4.

As shown in FIG. 2, when plug 16 is assembled for running into a well,wedge 62 is situated generally above slip 66. Preferably, to ensurereliable displacement of wedge 62 into slip 66 and to reduce the lengthof plug 16, lower end 70 of wedge 62 is received in upper end 96 of slip66 as shown. Thus, the smaller outer diameter portion of tapered outersurface 78 of wedge 62 engages the upper, larger inner diameter portionof tapered inner surface 102 of slip 66. Sealing ring 64 is carried ontapered outer surface 78 of wedge 62 near its lower end 70 and aboveslips 66. Preferably, as shown, sealing ring 64 abuts the upper end 96of slip 66.

Preferably the wedge and slip are releasably connected to each other toprevent unintended setting of the plug as it is run into a well. Forexample, as shown in FIG. 2, plug 16 is provided with a plurality ofshear pins 106. Shear pins 16 extend through radial bores 108 near theupper end 96 of slip 66 and into an annular groove 110 in the taperedouter surface 78 of wedge 62 near its lower end 70. Preferably, asshown, there is one shear pin 106 provided for each slip segment 112.Shear pins 106 serve as a frangible retainer which prevents relativemovement between wedge 62 and slip 66 as plug 16 is run into a well, butallows movement when a predetermined actuating force is applied acrossshear pins 66. Shear pins 66 made be made of relatively soft metals,such as brass or aluminum. It will be appreciated, however, that anynumber of frangible connectors are known in the art and may be used toreleasably connect wedge 62 and slip 66.

FIG. 3 shows plug 16 after it has been set in liner 4. As will beappreciated by comparing FIG. 3 to FIG. 2, shear pins 106 have beensheared and wedge 62 has been driven into sealing ring 64 and slip 66.Wedge 62 has traveled axially downward to a point where sealing ring 64is now proximate to the upper end 68 of wedge 62. As wedge 62 travelsaxially downward, the complementary tapers on outer surface 78 of wedge62 and on ring bore 84 and inner surface 102 of slip 66 allow wedge 62to ride under sealing ring 64 and slip 66. As wedge 62 rides undersealing ring 64 and slip 66, it forces them to expand radially fromtheir nominal run-in outer diameters.

In accordance with a preferred aspect of the subject invention, body 82of sealing ring 64 is fabricated from a sufficiently ductile material toallow sealing ring 64 to expand radially into contact with liner 4without breaking. As sealing ring 64 expands radially, outer elastomericseal 92 seals against liner 4 and inner elastomeric seal 94 sealsagainst outer surface 78 of wedge 62. Sealing ring 64 is thus able toprovide a seal between plug 16 and liner 4.

As slip 66 is expanded radially by wedge 62 at least some of thefrangible portions 114 between slip segments 112 break, allowingindividual slip segments 112 to expand further into contact with liner4. Slip segments 112, therefore, are able to anchor plug 16 within liner4. Upper end 96 of slip 66 abuts the lower end of sealing ring 64, thusalso providing hard backup for sealing ring 64 as it expands radially toseal against liner 4.

Once plug 16 has been sealed and anchored in liner 4, a frac ball may beflowed into well 1 to restrict the flow of fluid through plug 16 and tosubstantially isolate portions of well 1 below plug 16. Morespecifically, as shown in FIG. 4, a frac ball 76 may be deployed ontoseat 74. As best seen in FIGS. 3 and 5, ball seat 74 provides a beveledshoulder upon which ball 76 will rest. Moreover, as seen in FIGS. 3 and4, when wedge 62 has been fully inserted into slip 66, ball seat 74 issituated axially between the upper end of sealing ring 64 and the lowerend 98 of slip 66. More specifically, ball seat 74 is situated axiallyproximate to, and almost directly inward of sealing ring 64. Thus, whenhydraulic pressure is applied to ball 76, a portion of the forcetransmitted from ball 76 to wedge 62 will be directed radially outwardthrough sealing ring 64. Moreover, given the circular contact pointbetween ball 76 and seat 74, that force will be directed uniformlyoutward through the circumference of seat 74. The force transmittedthrough ball 76 and seat 74 will help ensure that sealing ring 64maintains an effective seal between plug 16 and liner 4.

Other closure devices and arrangements, however, may be used in thenovel plugs. For example, a standing valve may be used to restrictpassage through the wedge bore. Non-spherical closure devices may beused as well, along with non-circular seats and wedge bores. Moreover,as used herein, the term “bore” is only used to indicate that a passageexists and does not imply that the passage necessarily was formed by aboring process or that the passage is axially aligned with the well boreor tool.

Similarly, outer surface 78 of wedge 62, bore 84 of sealing ring 64, andbore 100 of slip 66 all have been described as having an invertedtruncated conical shape. It will be appreciated, however, that themating tapered surfaces of wedge 62, sealing ring 64, and slip 66 mayhave different geometries. Wedge 62, for example, may be provided with anumber of discrete, flat ramped surfaces arrayed circumferentially aboutits outer surface 78. Such ramps may be visualized as bevels or asgrooves on a conical surface or, as the ix sides of a tapered prismhaving a polygonal cross-section. Bore 84 of sealing ring 64 and bore100 of slip 66 would be modified so that they mate with and accommodatewedge 62 as it is driven downward. For example, the novel plug may beprovided with discrete slip segments which ride up flat grooves ortracks provided in the wedge.

In general, the novel plugs may be fabricated from materials typicallyused in plugs of this type. Such materials may be relatively hardmetals, especially if removal of the plugs is not necessary, buttypically the materials will be relatively soft, more easily drilledmaterials. For example, wedge 62 and slip 66 may be fabricated fromnon-metallic materials commonly used in plugs, such as fiberglass andcarbon fiber resinous materials. The components may be molded, but moretypically will be machined from wound fiber resin blanks, such as awound fiberglass cylinder. Alternately, suitable wedges and slips may befabricated from softer or more brittle metals that are easier to drill.For example, slip 66 may be fabricated from surface hardened cast iron,especially cast iron having a surface hardness in the range of 50-60Rockwell C. Such materials and methods of fabricating wedge and slipcomponents are well known in the art and may be obtained commerciallyfrom many sources.

As noted, the sealing ring in the novel plugs preferably are fabricatedfrom a sufficiently ductile material so as to allow the ring to expandradially into contact with a liner without breaking. For example, ringbody 82 may be fabricated from aluminum, bronze, brass, brass, copper,mild steel, or magnesium and magnesium alloys. Alternately, the ringbody may be made of hard, elastomeric rubbers, such as butyl rubber.

Preferably, however, the sealing ring is fabricated from a plasticmaterial. Plastic components are more easily drilled and the resultingdebris more easily circulated out of a well. Engineering plastics, thatis, plastics having better thermal and mechanical properties than morecommonly used plastics, are preferred. Engineering plastics that may besuitable for use include polycarbonates and Nylon 6, Nylon 66, and otherpolyamides, including fiber reinforced polyamides such as Renypolyamide. “Super” engineering plastics, such as polyether ether ketone(PEEK) and polyetherimides such as Ultem®, are especially preferred.Mixtures and copolymers of such plastics also may be suitable. Preferredmaterials generally will have useful operating temperatures of at least250° F., and preferably at least 350° F., and a tensile strength of aleast 5,000 psi, preferably at least about 1,500 psi. Such preferredmaterials also generally will provide the ring body with an elongationfactor of at least 10%, and preferably at least 30%.

As noted above, the sealing ring may be provided with elastomericmaterial around its outer or inner surface. Such elastomeric materialsinclude those commonly employed in downhole tools, such as butylrubbers, hydrogenated nitrile butadiene rubber (HNBR) and other nitrilerubbers, and fluoropolymer elastomers such as Viton.

Overview of Preferred Tool String

The novel plugs typically will be run into a well as part of a toolstring 10 which includes a perf gun 11, setting tool 12, and adapter kit14 as shown schematically in FIG. 1A. Perf gun 11, as noted above, isused to perforate liner 4. Adapter kit 14 releasably connects andtransmits setting force from setting tool 12 to plug 16. Tool string 10also may incorporate additional tools to facilitate the fracturingoperation or to perform additional operations. For example, sinker bars,centralizers, rope sockets, pump down fins, and collar locators may beincorporated into tool string 10.

Tool string 10, as described above, may be run into well on wireline 15.Wirelines are heavy cables that include electrical wires through which atool, such as perf gun 11 and setting tool 12, may be actuated orotherwise controlled. Fluid will be pumped into the well to carry thetools to the desired location in the liner. Other conventionalequipment, however, such as coiled tubing or pipe, may be used to deploythe novel plugs and tool strings in a liner.

FIGS. 9-16 show setting tool 12, adapter kit 14, and plug 16 in greaterdetail during various stages of deploying and operating those tools,with FIGS. 9-12 showing the tools 12/14/16 as they are run into a well.As may be seen therein, plug 16 is coupled at its upper end to adapterkit 14 which is connected to setting tool 12.

A variety of setting tools and adapter kits may be used with the novelplugs. For example, setting tool 12 is a pyrotechnic “Baker Style”setting tool similar to the E-4 series pyrotechnic setting tools sold byBaker Hughes. It has combustible powder charges which are electricallyignited through a wireline. Ignition of the charges generates pressurethat will actuate the tool. Other pyrotechnic setting tools, however,may be used, such as the Compact wireline setting tools sold by Owen OilTools, the GO-style setting tools available from The Wahl Company, andthe Shorty series tools available from Halliburton. Likewise, othertypes of setting tools may be used. For example, electrohydraulicsetting tools, such as Weatherford's DPST setting tool, may be used.Hydraulic setting tools, such as Schlumberger's Model E setting tool, orball activated hydraulic setting tools, such as Weatherford's HSTsetting tool and American Completion Tools Fury 20 setting tools, alsomay be used. If hydraulic setting tools are used, the tools will be runin a coiled tubing or a pipe string.

Details of the construction and operation of such setting tools are wellknown in the art and will not be expounded upon. Suffice it to say,however, that setting tool 12 includes an inner part 18 and an outerpart 20, as may be seen in FIGS. 9-10. When setting tool. 12 isactuated, outer part 20 moves downward relative to inner part 18transmitting actuating force through adapter kit 14 to plug 16.

Likewise, various adaptor kits may be used with the novel plugs, thespecific design of which will be tailored to a particular setting tool.Adapter kit 14, for example, generally includes a setting tool adapter26, a top cap 24, an inner mandrel 22, a collet or release sleeve 32, anadjusting sleeve 54, and an outer setting sleeve 52. Adapter 26, top cap24, inner mandrel 22, and release sleeve 32 in general serve toreleasably connect plug 16 to inner part 18 of setting tool 12.Adjusting sleeve 54 and outer setting sleeve 52 serve generally totransmit downward movement of setting tool outer part 20 to plug 16.

As seen best in FIG. 11, inner mandrel 22 of adapter kit 14 has agenerally open cylindrical shape. It is connected to the lower end ofinner part 18 of setting tool 12 by setting tool adapter 26 and top cap24. Release sleeve 32 is carried on mandrel 22 and in turn carries plug16.

More particularly, mandrel 22 includes an upper cylindrical outersurface 28 and a lower, enlarged diameter cylindrical outer surface 30.Release sleeve 32 has an upper generally cylindrical portion defining aninner bore 34. Mandrel 22 extends through bore 34 of release sleeve 32,with release sleeve 32 being carried about the upper portion of outersurface 28 of mandrel 22. A plurality of collet arms 36 extend downwardfrom the upper portion of release sleeve 32. Each collet arm 36 includesa collet head 38. Collet heads 38 have a radially inward extendingprotrusion 40 and a radially outward extending protrusion 42. Radiallyinward surface 44 on inward extending protrusions 40 of collet heads 38slidably engage the lower, enlarged diameter outer surface 30 of mandrel22. It will be appreciated, therefore, that except at their heads 38,collet arms 36 are concentrically spaced radially outward of mandrel 22.

During operation of setting tool 12, mandrel 22 can slide freely withinbore 34 of release sleeve 32. Initially, however, mandrel 22 and releasesleeve 32 are releasably restricted from relative movement as they arerun into well 1. As described further below, the releasable connectionbetween mandrel 22 and release sleeve 34 prevents plug 16 from being setprematurely as it is run into a well. It can be broken after plug 16 isdeployed, however, to allow plug 16 to be installed and ultimately toallow setting tool 12 and adapter kit 14 to be released and withdrawnfrom plug 16.

Thus, as shown in FIG. 12, upper outer surface 28 of mandrel 22 has anannular groove 46, and the upper portion of release sleeve 32 has aplurality of radial bores 50. Shear pins 48 extend through radial bores50 and into groove 46, thus collectively providing what may be referredto as connector 48 and a frangible connection between mandrel 22 andrelease sleeve 32. Other frangible connections, however, may be usedwith other interfering geometries. For example, instead of groove 46 aseries of detents, spotfaces, or threaded, flat-bottomed, or throughholes may be machined into mandrel 22.

Outer setting sleeve 52 of adapter kit 14 is a generally cylindricalsleeve which is disposed about and radially spaced outward from mandrel22. As seen in FIG. 11, outer setting sleeve 52 is connected to thelower end of outer part 20 of setting tool 12 via an adjusting sleeve54. It will be appreciated that in their run-in, unset state, plug 16 iscarried on release sleeve 32 between collet heads 38 and outer settingsleeve 52.

More particularly, as seen best in FIG. 12, outer setting sleeve 52includes a downward facing lower end or setting surface 56. Settingsurface 56 is substantially normal or perpendicular to the longitudinalaxis 60 of the tools such that it can abut and bear on the upper end 68of plug wedge 62. Outward protrusion 42 of collet heads 38 have anupwardly facing setting surface 58. Setting surfaces 58 are tapereddownwardly and outwardly, thus mating with the upwardly and inwardlytaper surface 124 at the lower end 98 of plug slip 66.

It will be appreciated that the liner into which frac plugs are deployedmay not have a uniform diameter. There may be protrusions in the linerresulting from accumulation of debris, scale, and rust. The liner alsomay have manufacturing defects or dents and other damage caused by welloperations. Moreover, well fluids can contain solids and debris.Tolerances between the frac plug and the nominal inner diameter of theliner can be relatively small, leaving only a small gap allowing for thedownward travel of the plug and for the flow of fluid between the plugand liner. Thus, frac plugs can be susceptible to getting stuck,damaged, or prematurely set as they are deployed into a liner.

Accordingly, the novel plugs and tool strings preferably are providedwith gauge points or surfaces to facilitate deployment and to protectthe tool as it is deployed. Thus, as may be seen in FIG. 12, which showsplug 16 in its unset, run-in position, the outside diameter of wedge 62at its upper cylindrical outer surface portion. 80 is substantiallyequal to an outer diameter defined by outer surfaces 138 of collet heads38. The outside diameters of sealing ring 64 and slip 66 are less thanthe outside diameters of wedge outer surface portion 80 and collet headouter surface portions 138. Surfaces 80 and 138, therefore, serve asgauge points supporting plug 16 against liner 4 and minimizing contactbetween sealing ring 64 and slip 66 and liner 4 as plug 16 is deployedthrough liner 4. Preferably, the tolerances are such that it providessufficient clearance for plug 16 to be lowered past more typicallyencountered obstructions, protrusions, and bends in liner 4 withoutcatching or damage. Such protection is particularly important when plug16 is deployed into horizontally oriented portions of liner 4.

The outer surfaces of setting sleeve 52 of adapter kit 14 and outer part20 of setting tool 12 also preferably are treated with a frictionreducing material such as Teflon®, Xylan®, and other fluoropolymers orother similar materials. Such materials can reduce resistance todeployment of the tool string through a liner. Reducing resistance isparticularly helpful when the tool string is being pumped into orthrough a horizontal portion of a liner on a wireline.

Moreover, if tool string 10 will be pumped down liner 4 on wireline 15,and especially if it will be pumped into a horizontal extension of liner4, plug 16 preferably is provided with a pump down fin 144. As shown inFIG. 17, pump down fin 144 is attached to the lower end of mandrel 22 byan annular nut 146 threaded into threads 148 provided inside mandrel 22.It will be appreciated that pump down fin is sized such that it canslidingly engage liner 4 and thus assist in pumping tool string 10 intoliner 4. Pump down fin 144 also preferably is composed of a rubber orelastomeric material and is somewhat flexible so that, as described indetail below, it does not impede release or withdrawal of adapter kit 14from plug 16.

FIG. 13 shows adapter kit 14 and plug 16 after setting tool 12 has beenactuated to set plug 16 in liner 4. Specifically, it will be noted thatouter part. 20 of setting tool 12 and setting sleeve 52 of adapter kit14 have moved axially downward. Downwardly facing setting surface 56 ofsetting sleeve 52 and upwardly facing setting surface 58 on collet heads38 are aligned, thus allowing plug 16 to be compressed longitudinallytherebetween. More particularly, as described in detail above, wedge 62has been driven into sealing ring 62 and slip 66 to seal and anchor plug16 in liner 4.

It will be appreciated that wedge 62 is described as being displaceddownward into sealing ring 62 and slip 66 as plug 16 is set. Duringnormal operation of setting tool 12 wedge 62 will be driven downward inan absolute sense, that is, it will move further down liner 4 whilesealing ring 62 and slip 66 remain in place relative to liner 4. Inother words, wedge 62 will be driven into sealing ring 62 and slip 66,instead of sealing ring 62 and slip 66 being pushed up and over wedge62. If any of the tools hang up in liner 4, however, that may not bestrictly the case. Thus, “downward” movement of wedge 62 will beunderstood as relative to sealing ring 62 and slip 66.

FIG. 14 shows an initial stage of releasing and withdrawing adapter kit14 from set plug 16. As noted above, mandrel 22 and release sleeve 32 ofadapter kit 14 initially are restricted from moving relative to eachother by frangible connector 48. Frangible connector 48, however, issubjected to shear forces as plug 16 is set. Specifically, a downwardforce is applied by setting tool outer part 20 to release sleeve 32(through adapter kit setting sleeve 52, plug 16, and collet heads 38)and an upward force is applied by setting tool inner part 18 to mandrel22. After plug 16 is fully set, those shear forces will increase rapidlyuntil they exceed a predetermined setting force. It will be appreciated,of course, that the number, size, and composition of shear pins 50 orother frangible connectors may be varied to provide the desired upperlimit of setting force which can be applied to plug 16.

At that point, frangible connector 48 will shear, eliminating anyfurther compressive force on plug 16. As will be appreciated bycomparing FIG. 14 to FIG. 13, shearing of frangible connection 48 alsoallows mandrel 22 (and setting tool inner part 18) to begin movingupward relative to release sleeve 32 (and setting tool outer part 20).Release sleeve 32 at this point is still held in position by plug 16 bythe engagement of collet heads 38 with the lower end 98 of slip 66. Italso will be noted that pump down fin 144, if provided, will be deformedand will not impede travel of mandrel 22 upward through release sleeve32.

FIG. 15 shows an intermediate stage of releasing and withdrawing adapterkit 14 from set plug 16. As seen therein, mandrel 22 has continuedtraveling upward to a point where it engages collet sleeve 32. Inparticular, the outer, upward facing shoulder 140 on the lower end ofmandrel 22 now is bearing on an inner, downward facing shoulder 142 onthe upper end of release sleeve 32.

FIG. 16 shows a later stage of releasing and withdrawing adapter kit 14where mandrel 22 has pulled release sleeve 32 upward and partially outof set plug 16. That is, once mandrel 22 engages release sleeve 32 itwill pull release sleeve 32 up with it. Downward facing tapered lowersurface 124 on the lower end 98 of slip 66 and upward facing settingsurface portions 58 of collet heads 38 have complementary angles. Thus,upward motion of release sleeve 32 will cause collet heads 38 to camradially inward. Release sleeve 32 is thereby released from lateralengagement with slip 66 and can travel upward through inner bore 72 ofwedge 62.

Thus, it will be noted that in FIG. 16 release sleeve 32 has traveledupward and partially through plug 16. Setting tool 12 then can be pulledfurther out of liner 4 via setting tool inner part 18 or wireline 15such that adapter kit 14 and, in particular, release sleeve 32eventually is pulled completely out of plug 16. Plug 16 then will befully installed as depicted in FIG. 3 and will be ready to receive fracball 76 as depicted in FIG. 4. It will be noted that when adapter kit 14has been removed from plug 16, inner bore 72 of wedge 62 provides arelatively large conduit and is free of any structures substantiallyrestricting the flow of production fluids up through plug 16.

Assembly of Preferred Tool String

Preparing setting tool 12, adapter kit 14, and plug 16 for deploymentinto well 1 is perhaps best visualized by reference to FIG. 11. First,setting tool adapter 26 is threaded on to the lower end of inner part 18of setting tool. The threaded connection 132 may be secured by one ormore set screws (not shown).

Next, adjusting sleeve 54 is threaded to the lower end of the outer part20 of setting tool 12 and setting sleeve 52 is threaded onto adjustingsleeve 54. The threaded connection 130 between adjusting sleeve 54 andsetting tool outer part 20 may be secured by one or more set screws (notshown). The threaded connection 134 between setting sleeve 52 andadjusting sleeve 54 is configured such that it may be completely overrunby setting sleeve 52. When setting sleeve 52 overruns threadedconnection 134 it is free to slide upward past adjusting sleeve 54.

Mandrel 22 of adapter kit 14 then is inserted upwards through releasesleeve 32 and top cap 24 is threaded on to the upper end of mandrel 22.Threaded connection 126 between top cap 24 and mandrel 22 preferably issecured by one or more set screws 128. Shear pins 48 then are installedthrough bores 50 in release sleeve 32 and into groove 46 of mandrel 22to frangibly connect release sleeve 32 to mandrel 22.

The subassembly of mandrel 22, release sleeve 32, and top cap 24 then isinserted upward through the bore of plug 16 such that setting surfaceportions 58 of collet heads 38 bear on mating lower surface 124 of slip66. That subassembly, in turn, is connected to setting tool 12 by firstsliding setting sleeve 52 upward and past adjusting sleeve 54, therebyallowing access to setting tool adaptor 26. Tension lock spring 150 thenis inserted around the upper end of top cap 24, and top cap 24 isthreaded into adapter 26. Threaded connection 136 between top cap 24 andadapter 26 may be secured by one or more set screws (not shown). Tensionlock spring 150 also helps to prevent rotation between top cap 24 andadapter 26. As shown in FIG. 18, lock spring 150 has upper and lower endprongs 152 and 154 which engage radial recesses (not shown) in the lowerend of adapter 26 and in the upward facing shoulder of top cap 24.

Finally, setting sleeve 52 is slid back down over adjusting sleeve 54toward wedge 62 of plug 16. Once it again engages threaded connection134 with adjusting sleeve 54, setting sleeve 52 is rotated aboutthreaded connection 134 to move it downward until its lower end 56engages the upper end 68 of wedge 62. Setting sleeve 12, adapter kit 14,and plug 16 are now ready for deployment.

Overview of Second Preferred Plug

A second preferred embodiment 216 of the novel plugs is illustrated inFIGS. 19-33. Second preferred plugs 216 may be used to perform “plug andperf” fracturing operations in substantially the same manner asdescribed above for first preferred plugs 16 and schematic FIG. 1. Plug216 may be connected to setting tool 12 via an adapter kit 214. Thosetools then will be deployed into well 1 along with perf gun 11 viawireline 15. Setting tool 12 will be actuated to install plug 216 inliner 4 and to release adapter kit 214 from plug 216. Perf gun then willbe actuated to perforate liner 4, after which perf gun 11, setting tool12, and adapter kit 214 will be pulled out of well 1 by wireline 15.Fluid will be pumped into liner 4 to establish fractures 9 adjacent theperforations. The plugging and perfing will be repeated until fractures9 have been established in formation 6 along the length of liner 4.

As seen best in FIGS. 19-20 and 23, which show plug 216 in its run-instate, plug 216 generally comprises an annular wedge 262, a sealing ring264, an annular slip 266, a setting ring 270, and a gauge ring 280.Annular wedge 262 is shown in isolation in FIG. 21. As seen therein,wedge 262 is similar in respects to wedge 62 of plug 16. Wedge 262 alsomay be described in general terms as having an annular or opencylindrical shape. The upper portion of wedge 262 is generally tapered,but in contrast to wedge 62, the lower portion of wedge 262 comprises aplurality of collet fingers 268.

Collet fingers 268 are integrally formed with wedge 262 and extendaxially downward from the lower end of the wedge upper portion. Colletfingers 268 are spaced circumferentially around annular wedge 262 andterminate in collet heads 275. As will be appreciated from thediscussion that follows, collet fingers 268 provide support for slip 266as it is assembled and a base for connecting gage ring 280.

Wedge 262 also has an axial passage or bore 263 extending through itsupper portion. An inner ball seat 291 is defined in wedge bore 263, bore263 otherwise having a substantially uniform diameter.

The upper portion of wedge 262 has an outer, generally truncatedinverted conical surface 267. That is, outer conical surface 267 tapersdownwardly and inwardly, and the diameter of its upper end is greaterthan the diameter of its lower end. The upper end of wedge 262 may have,as does wedge 62 of plug 16, a substantially cylindrical outer surfaceif desired. That is, conical surface 267 does not necessarily extend allthe way to the upper end of wedge 262. Preferably, however, it extendsalong the substantially majority of the upper portion of wedge 262.

As best appreciated from FIGS. 19-20, sealing ring 264 of plug 216 isquite similar to sealing ring 64 in plug 16. Sealing ring 264 has arelatively short, annular body 288 defining an axial passage or bore.The ring bore has a generally inverted truncated conical shape, that is,it tapers radially outward from its lower end to its upper end. Theinner taper of the bore of sealing ring 264 is complementary to thetaper provided on outer conical surface 267 of wedge 262. Sealing ring264 preferably is provided with one or more elastomeric seals whichultimately will enhance the seal between plug 216 and liner 4 when plug216 is set. Thus, ring body 288 is provided with one or more outerelastomeric seals 284 in corresponding grooves on the outer surface ofring body 288. One or more inner elastomeric seals 286 are provided incorresponding grooves in the ring bore. Other seal configurations may beused, however, or the seals may be eliminated depending on the design ofthe sealing ring and the materials from which it is fabricated.

Slip 266 of plug 216, like slip 66 of plug 16, is designed to grip andengage liner 4. Slip 66, however, is a breakaway slip designed to breakapart into several segments. In contrast, slip 266 of plug 216 is anassembly of discrete, separate slip segments. More specifically, slip266 has six individual slip segments 266 a to 266 f. Individual slipsegments 266 a-f may be visualized as a lateral segment of an opencylinder. When plug 216 is in its run-in condition, as best appreciatedfrom FIGS. 20 and 22, segments 266 a-f are aligned along, and arrangedangularly about the tool axis. Preferably, slip segments 266 a-f areclosely adjacent or abut each other. Thus, slip segments 266 a-fcollectively define an open cylindrical slip 266 having an axial innerpassage or bore 274.

Bore 274 of slip 266 has a generally truncated inverted conical surface.That is, slip bore 274 tapers radially inward from top to bottom, andthe diameter of slip bore 274 at its upper end is greater than thediameter at its lower end. Preferably the taper in slip bore 274 iscomplementary to the taper on outer conical surface 267 of the upperportion of wedge 262.

The outer surface of slip 266 is generally cylindrical. Preferably, itis provided with features to assist slip 266 in engaging and grippingliner 4 when plug 216 is set. Thus, for example, slip 266 may beprovided with high-strength or hardened particles, grit or inserts, suchas buttons 265 embedded in its outer surface. Buttons 265 may be, forexample, a ceramic material containing aluminum, such as a fused aluminaor sintered bauxite, or rx zirconia, such as CeramaZirc available fromPrecision Ceramics. Buttons also may be fabricated from heat treatedsteel or cast iron, fused or sintered high-strength materials, or acarbide such as tungsten carbide. The precise number and arrangement ofbuttons 265 or other such members may be varied. The outer surface ofslip 266 also may be provided with teeth or serrations in addition to orin lieu of buttons or other gripping features.

In general terms, plug 216 will be set in liner 4 in the same manner asis plug 16. Annular wedge 262 will be driven into sealing ring 264 andannular slip 266. As wedge 262 is driven downward, it will force sealingring 264 and slip 266 to expand and seal and anchor 216 in liner 4. Theoperation of plug 216 may be understood in greater detail by comparingFIGS. 19-20 and 23 with FIG. 24. FIGS. 19-20 and 23 show plug 216 in itsrun-in condition. FIG. 24 shows plug 216 after it has been set in liner4 and frac ball 76 has seated in plug 216 to isolate lower portions ofliner 4.

As shown in FIGS. 19-20 and 23, when plug 216 is assembled for runninginto a well, slip 266 is disposed generally around collet fingers 268 ofwedge 262 with the upper end of slip 266 extending over the lowerportion of outer conical surface 267 of wedge 262. Outer conical surface267 of wedge 262 thus is received in and engages conical bore 274 ofslip 266.

Sealing ring 265 is carried on outer conical surface 267 of wedge 262near its lower end such that it abuts the upper end of slip 266. Slipsegments 266 a-f preferably are secured at their upper ends. Thus, forexample, the lower end of sealing ring 264 is provided with an annularprojection or lip 289. Slip segments 266 a-f have a complementary lip273 on their upper ends. Sealing ring lip 289 and slip lip 273 engageeach other, thus securing the upper end of slip 266.

Collet fingers 268 extend downward through slip bore 274 and terminatebeyond the lower end of slip 266. Setting ring 270 is carried slidablyaround that lower portion of collet fingers 268. More particularly, theupper end of setting ring 270 abuts the lower end of slip 266 and thelower end of setting ring 270 abuts heads 275 of collet fingers 268 andan upward facing shoulder on gauge ring 280.

Setting ring 270 is shown in isolation in FIGS. 25-26. As shown therein,setting ring 270 has a generally annular body 277 having a plurality ofkeys 271. Keys 271 are arranged circumferentially on the inner surfaceor bore of setting ring body 277 and protrude radially inward. Settingring 270 is slidably carried around the lower portion of collet fingers268 such that keys 271 on setting ring 270 extend inward into slots 269between collet fingers 268.

As shown in FIGS. 19-20 and 23, gauge ring 280 may be viewed as a bottomcap for plug 216. It is attached to the lower end of collet fingers 268and extends generally around setting ring 270 and the lower end of slip266. More particularly, and referring to those figures and to FIGS.27-28 which show gauge ring 280 in isolation, it will be appreciatedthat the lower portion of gauge ring 280 is generally enlarged and fitsaround and below heads 275 of collet fingers 268. Gauge ring 280 may beconnected to heads 275 of collet fingers 268, for example, by fasteners285 shown in FIG. 20. Fasteners' 285 may be screws, bolts, or pinsinserted through radial holes 283 in the lower portion of gauge ring 280(see FIG. 27) into radial holes 276 provide in collet heads 275 (seeFIG. 21).

Gauge ring 280 also has a relatively thin upper perimeter wall or skirt282 extending upwardly from its lower portion. Skirt 282 extendsupwardly beyond setting ring 270 and terminates just beyond the lowerend of slip 266. Gauge ring 280 and, in particular, skirt 282 is thusable to hold the lower portions of slip segments 266 a-f together in aclose annular arrangement.

Gauge ring 280 also helps protect the lower end of plug 216 as it isdeployed into a well. Skirt. 266 of gauge ring 280 extends around thelower portions of slip segments 266 a-f, thus helping to protect themfrom catching on debris, protrusions, and the like that might cause themto deploy prematurely. It also will be noted that the outer diameter ofgauge ring 280 is greater than the outer diameter of the setting ring270, slips 266, sealing ring 264, and the upper portion of wedge 266.More particularly, the outer diameter of gauge ring 280, relative to theinner walls of liner 4, is such that it presents a leading edgesufficient to prevent plug 216 from being lowered into constrictions inliner 4 that are too narrow to allow passage of plug 216. Preferably,the tolerances are such that it provides sufficient clearance for plug216 to be lowered past more typically encountered obstructions,protrusions, and bends in liner 4 without catching or damage.

Plug 216 may be deployed and installed in much the same manner as plug16. As shown in FIGS. 29-30, plug 216 is coupled at its upper end tosetting tool 12 and adapter kit 214. Setting tool 12, as noted above,includes inner part 18 and outer part 20. When actuated, outer part 20moves downward relative to inner part 18 and transmits force throughadapter kit 214 to plug 216.

Adapter kit 214 generally includes setting tool adapter 26, a top cap224, an actuating mandrel 222, adjusting sleeve 54, outer setting sleeve52, and a sleeve adapter 210. Adapter 26, top cap 224, and actuatingmandrel 222 in general serve to releasably connect plug 216 to innerpart 18 of setting tool 12. Adjusting sleeve 54, outer setting sleeve52, and sleeve adapter 210 serve generally to transmit downward movementof setting tool outer part 20 to plug 216.

Actuating mandrel 222 of adapter kit 214 has a generally opencylindrical shape. As shown in FIG. 29, it is connected to the lower endof setting tool inner part 18 by setting tool adapter 26 and top cap224. Mandrel 222 is releasably connected at its lower end to plug 216.As described further below, that releasable connection allows plug 216to be set and ultimately allows setting tool 12 and adapter kit 214 tobe released and withdrawn from plug 216.

More particularly, when plug 216 is run into a well mandrel 222 isreleasably connected to setting ring 270 of plug 216 by a plurality offrangible fasteners 278. Frangible shear screws 278 extend throughthreaded radial holes 272 (see FIGS. 25-26) in keys 271 of setting ring270 and into recesses such as grooves 290 (see FIG. 31) at the lower endof mandrel 222. Shear screws 278 will be designed to break at a desiredshear force and thereby release mandrel 222 from plug 216 after it hasbeen installed in liner 4. Other frangible connectors, such as pins, maybe used for such purposes. Similarly, instead. H of grooves 290, mandrel222 may be provided with a series of detents, spotfaces, or holes.

As noted above, outer setting sleeve 52 of adapter kit 214 is connectedat its upper end to the lower end of outer part 20 of setting tool 12via adjusting sleeve 54. The lower end of outer setting sleeve 52 abutsand is connected to sleeve adapter 210. For example, the upper end ofsleeve adapter 210 may be threaded into the lower end of outer settingsleeve 52. Set screws or the like (not shown) may extend through radialholes 240 in the lower end of outer setting sleeve 52 and into holes, agroove, or other outer recess 211 in sleeve adapter 210 (see FIG. 33).

Sleeve adapter 210 is slidably carried about the lower, enlarged end oftop cap 224. When plug 216 is in its run-in state, however, sleeveadapter 210 and top cap 224 are releasably restricted from relativemovement. Thus, for example, frangible screws, pins, or other suitableconnectors 242 may extend through radial holes 212 in the lower end ofsleeve adapter 210 and into a groove 213 or other detents, spotfaces, orholes machined into the outer surface of top cap 224 (see FIG. 32). Asdescribed further below, the releasable connection between sleeveadapter 210 and top cap 224 prevents plug 216 from being set prematurelyas it is run into a well, but it can be broken after plug 216 isdeployed to allow plug 216 to be installed.

Once coupled to adapter kit 214 and setting tool 12, plug 216 may bedeployed and installed in a well. Though there are differences in theoperation, plug 216 will be installed in liner 4 generally in the samemanner as is plug 16. Annular wedge 262 will be driven into sealing ring264 and annular slip 266 to force sealing ring 264 and slip 266 toexpand and set and seal plug 216 in liner 4 as shown in FIG. 24.

More particularly, once plug 216 is deployed to the desired location inliner 4, setting tool 12 will be actuated. Once a predetermined force isgenerated within setting tool 12, the frangible connection betweensleeve adapter 210 and top cap 224 of adapter kit 214 will be broken.Setting tool outer part 20, adjusting sleeve 54, outer setting sleeve52, and sleeve adapter 210 then are able to move downward relative tosetting tool inner part 18, setting tool adapter 26, top cap 224, andmandrel 222.

Sleeve adapter 210 bears down on the upper end of wedge 262 which, asnoted above, carries sealing ring 264 and extends through slip 266 andsetting ring 270. Sealing ring 264 abuts the upper end of slip 266, andsetting ring 270 abuts the lower end of slip 266. Setting ring 270 isheld in position by mandrel 222, to which it is connected by frangiblefasteners 278. Collet fingers 268 of wedge 262, however, are able toslide freely within the bore of setting ring 270. That will allow plug216 to be installed, in essence, by compressing wedge 262, sealing ring264, and slip 266 together between sleeve adapter 210 and setting ring270.

More particularly, wedge 262 will be driven downward into sealing ring264 and slip 266. As wedge 262 travels axially downward, thecomplementary conical surfaces on the upper portion of wedge 262 and inthe bore of sealing ring 265 and bore 274 of slip 266 allow wedge 262 toride under sealing ring 264 and slip 266. As wedge 262 rides undersealing ring 264 and slip 266, it forces them to expand radially.

In accordance with a preferred aspect of the subject invention, body 288of sealing ring 264 is fabricated from a sufficiently ductile materialto allow sealing ring 264 to expand radially into contact with liner 4without breaking. As sealing ring 264 expands radially, outerelastomeric seal 284 seals against liner 4 and the inner elastomericseal 286 seals against the outer conical surface 267 of wedge 262.Sealing ring 264 is thus able to provide a seal between plug 216 andliner 4.

As slip 266 is expanded radially by wedge 262, slip segments 266 a-fwill be forced radially outward and eventually into contact with liner4. Thus jammed between outer conical surface 267 of wedge 262 and liner4, they are able to anchor plug 216 within liner 4. Upper end of slip266 abuts the lower end of sealing ring 264, thus also providing hardbackup for sealing ring 264 as it expands radially to seal against liner4.

As noted above, mandrel 222 is releasably connected to setting ring 270by frangible fasteners 278. When wedge 262 has been fully driven intosealing ring 264 and slip 266, a downward facing, beveled shoulder atthe lower end of upper portion of wedge 262 will engage setting ring270. Sealing ring 264 and slip 266 also will have been expanded intoengagement with liner 4. At that point the shear forces across frangiblefasteners 278 will increase rapidly. When those forces exceed apredetermine limit, frangible fasteners 278 will shear, relieving anyfurther compressive force on plug 216. Shearing of fasteners 278 alsoreleases mandrel 222 from setting ring 270. Inner part 18 of settingtool 12 will continue its stroke, pulling mandrel 222 upward.Preferably, the stoke of setting tool 12 will be such that mandrel 222is withdrawn to a point where its lower end is within the enlargediameter portion of wedge bore 263 above ball seat 291. Adapter kit 214and setting tool 12 then can be pulled out of plug 216 and liner 4 viawireline 15.

FIG. 24 shows plug 216 after it has been installed in liner 4 and fracball 76 has been deployed. Frac ball 76 has landed on seat 291 in bore263 of wedge 262. Seat 291 has a beveled surface which allows ball 76 tosubstantially restrict or preferably to shut off fluid flow through plug216, thereby substantially isolating portions of well 1 below plug 216.Preferably, when plug 216 is installed, seat 291 will be located at alevel between the upper and lower ends of slip 266.

For example, as appreciated from FIG. 24, seat 291 is situated withinbore 263 of wedge 262 such that when wedge 262 has been driven fullydownward it is disposed below the mid-point of slip 266 and well belowsealing ring 264. Thus, when fluid is pumped into liner 4 hydraulicpressure will build not only against frac ball 76, but also within asubstantial portion of wedge bore 263. The hydraulic pressure withinwedge bore 263 will bear radially outward through wedge 262, therebyenhancing the seal between sealing ring 264 and liner 4 as well as theengagement of slip 266 with liner 4. The shallow bevel on ball seat 291also allows ball 76 to transmit a substantial portion of the hydraulicpressure applied to it radially outward through wedge 262 to slipsegments 266 a-f, further enhancing the anchoring of plug 216 in liner4.

As described above with respect to plug 16, various modifications may bemade to illustrative plug 216. Other closure devices and arrangementsmay be provided. Standing valves and non-spherical closure devices maybe used. Wedge 264 may have a break-away configuration, or it may beconfigured to provide discrete ramped surfaces.

Plug 216 also may be fabricated from materials typically used in plugsof this type, and preferably will be softer, more easily drilledmaterials. Wedge 262 and slip 266, for example, preferably are machinedfrom wound fiber resin blanks, such as a wound fiberglass cylinder. Body288 of sealing ring 264 also preferably is fabricated from a ductilematerial, especially ductile plastics as described above for sealingring 64.

Plug 216 can be assembled from its component parts and prepared fordeployment into liner 4 as follows. First, setting tool adapter 26 isthreaded on to the lower end of inner part 18 of setting tool, adjustingsleeve 54 is threaded to the lower end of the outer part 20 of settingtool 12, and setting sleeve 52 is threaded onto adjusting sleeve 54, allas described above in relation to plug 16. Next, sleeve adapter 210 maybe threaded into the lower end of outer setting sleeve 52.

Plug 216 then may be assembled in an upside-down fashion. Specifically,annular wedge 262 may be inverted with collet fingers 268 pointing up.Sealing ring 264, with ring lip 289 facing up, then is passed overcollet heads 275 and slid down onto outer surface 267 of wedge 262. Withsealing ring 264 resting on wedge 262, slip segments 266 a-f then may beloaded (upside down) around wedge 262 such that lip 273 of each segment266 a-f engages lip 289 of sealing ring 264. Setting ring 270 then ispassed (upside down) over collet heads 275 and slid down wedge 262 withring keys 271 traveling through slots 269 between collet fingers 268until it abuts slip segments 266 a-f. Gauge ring 280 then can beconnected to heads 275 of collet fingers 268, for example, by fasteners285. Skirt 282 of gauge ring 280 will extend around and past settingring 270 such that it is able to hold slip segments 266 a-f in theirannular arrangement. Plug 216 now is ready for attachment to adapter kit214 and, thereby, to setting tool 12.

First, mandrel 222 is releasably connected to plug 216. Specifically,top cap 224 is threaded onto mandrel 222 as described above for plug 16.The threaded connection preferably is secured, e.g., by set screws 228or the like as may be inserted through radial holes 229 in top cap 224and into groove 230 on mandrel 222. Mandrel 222 then is inserted intobore 263 of wedge 262 such that grooves 290 at the lower end of mandrel222 are aligned with radial holes 272 in keys 271 of setting ring 270.Frangible shear screws 278 then are screwed into setting ring holes 272and into mandrel grooves 290. It will be noted that gauge ring 280 isprovided with openings 281 seen best in FIG. 27. Openings 281 allowsighting and alignment of setting ring holes 272 and mandrel grooves 290and insertion of shear screws 278.

Setting sleeve 52 and sleeve adapter 224 then can be raised to allowaccess to setting tool adapter 26. Top cap 224 now can be threaded intosetting tool adapter 26 as described above in relative to plug 16.Finally, setting sleeve 52 and sleeve adapter 224 are slid downwarduntil the lower end of sleeve adapter 224 abuts the upper end of wedge262. Sleeve adapter 210 then is releasably connected to top cap 224 byfrangible connectors 240 extending through radial holes 212 in the lowerend of sleeve adapter 210. Setting tool 12, adapter kit 224, and plug216 now are ready for deployment into a well.

It will be appreciated from the foregoing description of preferred plugs16 and 216 that the novel plugs share certain general features withprior art plug designs, but in general incorporate fewer parts. Theyrely on three primary components, a wedge, a sealing ring, and a slip,and design features which allow those three components to perform theessential functions of sealing and anchoring the plug. They do not relyon a central support component, such as a support mandrel, to supportthe wedge, sealing element, and slips as do conventional plugs, eitherduring setting of the plug or after it has been installed. Instead, asdescribed further below, the wedge in the novel plugs isself-supporting, and the wedge provides the support for the sealing ringand slip. No special backup rings, as are common in conventional plugs,are required to protect the sealing ring against extrusion. The slips inthe novel plugs provide a dual function of anchoring the plug andproviding a hard backup for the sealing ring. Thus, in general, they maybe more easily and economically fabricated and assembled.

Moreover, primarily because they do not incorporate a support mandrel,the novel plugs may have a relatively large central bore. The centralbore also is free of any structure which might substantially restrictflow of production fluids up through the plug. Thus, the novel plugs mayallow an operator to use dissolvable frac balls. After the ballsdissolve, the well may be produced without the considerable time andexpense of drilling out the plugs. The novel plugs also may facilitateunexpected remedial operations which must be performed through the plugbefore it is removed.

For a given liner size, the central bore in the wedge and slip of thenovel plugs will be larger than the central passageway in the supportmandrel of conventional designs. Thus, by essentially eliminating thesupport mandrel, the novel plugs provide a central passageway for fluidswhich is relatively larger. For example, conventional plugs for 0.3installation in a 5.5″ liner typically will have a central passagewaythrough the support mandrel of approximately 1″ in diameter. Incontrast, the novel plugs may have an internal diameter of approximately3″.

The large central bore relative to the length of the wedge and theoverall length of the plug is particularly important when the wedge andslip are fabricated from drillable composites such as wound fiberglass.Wound fiberglass has fibrous cords which are wound around a cylindricalcore and impregnated with resin. Manufacturers have developed variouswinding patterns designed to minimize this, but such materials areparticularly susceptible to axial shear stress. They may be visualizedas having a spiral shear plane running axially through the part, withthe inner portions of the spiral being the weakest. Thus, when pressureis applied behind a seated ball, shear forces will be transmittedaxially into the part through the seat. Excessive pressure can “blow”the ball through the part, essentially shearing away internal layers ofthe bore.

In conventional designs, the ball seat is provided in a relativelysmaller bore of a support mandrel. The shear forces, therefore, will beapplied through a smaller circumference where the support mandrel ismore susceptible to shearing. In order to compensate for the relativeweakness of the support mandrel, the support mandrel typically will berelatively elongated. The proportionally greater length provides therequisite resistance to shearing.

In contrast, the shallow bevel on ball seat 74/291 in plug 16/216 allowsshortening of the parts. That is, the shallow bevel on ball seat 74/291allows ball 76 to transmit a substantial portion of the hydraulicpressure applied to it radially outward. That not only enhances sealingand anchoring of plug 16/216, as discussed above, but it also means thata smaller vector component of the force applied to ball 76 istransmitted axially to wedge 62/262. Those parts may be made shorter asthe amount of shear stress which they must resist is reduced.Accordingly, the novel plugs will have ball seats wherein the bevel isfrom about 10° to about 30°, preferably about 15° off center.

It will be appreciated that it is possible for the novel plugs toeliminate the support mandrel typically incorporated into conventionalplugs primarily because of the taper applied to the wedge and slip andthe location of the ball seat within the wedge. For example, the taperangle on wedges 62/262 and slips 66/266 in plugs 16/216 is relativelyshallow. Preferably, the taper on the wedges and slips of the novelplugs is such that the wedges and slips are self-locking as opposed toself-releasing. With hard materials, such as steel, the upper limit forself-locking tapers is about 7°. With softer, more elastic materials,such as the preferred composite materials, steeper taper angles stillwill be self-locking. Accordingly, when fabricated from preferredcomposite materials the taper on the wedges and slips typically will befrom about 1° to about 10°, preferably about 4° off center. Conventionalplugs typically incorporate wedges and slips where the mating taper isrelatively steep, usually self-releasing. Thus, a relatively thick,strong support mandrel is required to back up the wedge and slip toensure that they do not separate and, thereby, compromise the seal oranchor of the plug.

Locating the ball seat within the bore and below the upper end of thewedge also helps minimize the need for support otherwise provided by asupport mandrel. For example, and regarding preferred plug 216, ballseat 291 is situated within bore 263 of wedge 262 well below the upperend of wedge 262. When wedge 262 is set, ball seat 291 is located belowthe axial midpoint of slip 266. Hydraulic pressure behind a seated ball76, therefore, will build within and bear radially outward through wedgebore 72 providing support for wedge 262 which in turn will enhance thesupport provided by wedge 262 to both sealing ring 264 and slip 266.

Shorter plugs are more easily deployed into liners, especially deviatedliners, and other factors being equal, may be drilled more quickly.Eliminating the support mandrel also helps to shorten the overall lengthof the novel plugs. The support mandrel typically is the longestcomponent in conventional plugs. Conventional plugs also typicallyrequire a pair of wedges and slips in order to maintain the radialexpansion of the elastomeric sealing element against the liner wall. Incontrast, the novel plugs preferably incorporate a single wedge andslip. Moreover, the sealing ring, carried as it is on the wedge, adds nolength to the novel plugs.

Though perhaps not as readily apparent, seating a ball within the wedgealso can help shorten the length of the novel plugs. For example, theupper end of wedge 262 and the lower end of gage ring 280 may beprovided with mating geometries, such as castellations 292 on wedge 262and castellations 293 on gauge ring 280. Castellations 292/293 helpminimize “spinning” and speed up drill out of a series of plugs 216.That is, if the remains of an upper plug 216 start to spin as materialis drilled away, the bit will push the upper plug 216 down until thecastellations 293 on the remnants of uphole plug 216 engage thecastellations 292 on a still set, downhole plug 216. The remnants ofplug 216 will stop spinning and may be drilled away.

The provision of castellations, bevels, or other mating geometries atthe ends of plugs is well known. Many conventional plugs, however,locate the ball seat at the top of the support mandrel. A seated ball,therefore, actually serves as a bearing surface to encourage spinning ofa plug remnant pushed down onto the ball. Other plugs may provide a ballseat within the support mandrel bore, but typically it is located abovethe level of the wedge. That placement essentially means that thesupport mandrel has been lengthened to allow mating geometric featuresto extend above the ball. In contrast, by locating ball seat 291 of plug216 well inside wedge bore 263, mating geometries may be provided onwedge 262 with minimal or essentially no lengthening of wedge 262.

Indeed, it will be appreciated that the novel plugs may be drilled moreeasily and will produce less material than conventional frac plugsoffering comparable performance, even conventional composite plugs. Allof the components may be made of easily drillable composite materialsor, in the case of the sealing ring, from plastics. As noted, thesupport mandrel is eliminated, eliminating what often is the singlelargest component in conventional composite plugs. The overall reduceddimensions of the novel plugs mean there is less material present in theplug. Especially when a large number of plugs must be drilled out, otherfactors being equal less material can mean much faster drilling timeswith far less debris which must be circulated out of the well.

For example, consider the Obsidian® frac plugs available fromHalliburton and the Diamondback frac plugs available from Schlumberger.Those are all composite frac plugs like preferred embodiments of thesubject invention. It will be appreciated that plug 216 sized for a 5.5″liner has only about 20% of the volume of material as in comparablysized Obsidian and Diamondback plugs.

Preferred embodiments of the sealing ring in the novel plugs also canfacilitate drilling in two other ways. As compared to sealing elementsin conventional plugs, sealing rings 64/264 in plugs 16/216 are muchsmaller and will produce less debris when drilled out. Sealing rings64/264 are relatively small even when composed of more easily drilledplastic material instead of soft metals.

Sealing elements in conventional plugs, as well as plastic sealing rings64/264 in novel plugs 16/216, are subject to extrusion if not when theplug is set, then when the plug is later exposed to hydraulic pressureduring fracturing operations. That is, hydraulic pressure will bear downon the seal. That pressure can open up channels in the seal or even pushthe seal material out from around the plug. Thus, conventional plugsincorporate various backup rings which are designed to back up thesealing element and minimize extrusion.

Typically, backup rings are made of relatively thin, somewhat flimsymetal which still allows what is viewed as a manageable amount ofextrusion. Manageable extrusion, in turn, necessarily means the sealingelement must be somewhat larger and comprise more material. Havingring-like shapes, conventional backup rings also become entangled arounda bit. Many such rings might be “gathered” by the bit as it works itsway through multiple plugs.

Sealing rings 64/264 of novel plugs 16/216, however, even when made ofplastic, comprise less ductile and, therefore, less extrudable material.Moreover, sealing rings 64/264 are provided with hard backup from slips66/266. For example, when plug 216 is in its run-in condition, segments266 a-f are closely adjacent and preferably abut each other.Collectively, slip segments 266 a-f define an open cylinder the upperend of which abuts the lower end of sealing ring 264. Segments 266 a-f,therefore, provides continuous support for sealing ring 264 as wedge 262starts to expand sealing ring 264 radially outward. Even when completelyset, from a cross-sectional perspective, slip segments 266 a-f haveseparated only a relatively short distance. Thus, slip segments 266 a-fcan provide near continuous, hard backup for sealing ring 264 and,thereby, minimize the likelihood of significant extrusion of sealingring 264 during fracturing operations. Importantly, they do so withoutincorporating metallic backup rings which later can complicate drillingof plugs.

It also has been observed that due to the contact between the lower endof sealing ring 264 and the upper end of slip segments 266 a-f, segments266 a-f expand radially more uniformly as wedge 262 is driven intosegments 266 a-f. It also will be appreciated that the inner and outerradii of slip segments 266 a-f preferably are matched, respectively,with the outer radii of the upper portion of wedge 262 and the innerdiameter of liner 4. Consequently, there is more uniformly distributedcontact between slip segments 266 a-f and the inner wall of line 4. Inparticular, the contact between buttons 265 will be more uniformlydistributed around plug 216, and the degree of contact between eachbutton 265 will be more uniform from button 265 to button 265.

Though described to a certain extent, it will be appreciated that novelplugs 16 and 216, along with setting tool 12 and adapter kits 14 and214, along with other embodiments thereof, may incorporate additionalshear screws and the like to immobilize components during assembly,shipping, or run-in of the plug. Additional set screws and the like maybe provided to prevent unintentional disassembly. Other sealing elementsmay be provided between components, and various ports accommodatingfluid flow around and through the assembly also may be provided. Suchfeatures are shown to a certain degree in the figures, but their designand use in tools such as the novel plugs is well known and well withinthe skill of workers in the art. In many respects, therefore, discussionof such features is omitted from this description of preferredembodiments.

Plugs 16 and 216 and other embodiments have been described as installedin a liner and, more specifically, a production liner used to fracture awell in various zones along the well bore. A “liner,” however, can havea fairly specific meaning within the industry, as do “casing” and“tubing.” In its narrow sense, a “casing” is generally considered to bea relatively large tubular conduit, usually greater than 4.5″ indiameter, that extends into a well from the surface. A “liner” isgenerally considered to be a relatively large tubular conduit that doesnot extend from the surface of the well, and instead is supported withinan existing casing or another liner. It is, in essence, a “casing” thatdoes not extend from the surface. “Tubing” refers to a smaller tubularconduit, usually less than 4.5″ in diameter. The novel plugs, however,are not limited in their application to liners as that term may beunderstood in its narrow sense. They may be used to advantage in liners,casings, tubing, and other tubular conduits or “tubulars” as arecommonly employed in oil and gas wells.

Likewise, while the exemplified plugs are particularly useful infracturing a formation and have been exemplified in that context, theymay be used advantageously in other processes for stimulating productionfrom a well. For example, an aqueous acid such as hydrochloric acid maybe injected into a formation to clean up the formation and ultimatelyincrease the flow of hydrocarbons into a well. In other cases,“stimulation” wells may be drilled near a “production” well. Water orother fluids then would be injected into the formation through thestimulation wells to drive hydrocarbons toward the production well. Thenovel plugs may be used in all such stimulation processes where it maybe desirable to create and control fluid flow in defined zones through awell bore. Though fracturing a well bore is a common and importantstimulation process, the novel plugs are not limited thereto.

The novel plugs also may incorporate additional closure devices. Forexample, a standing valve may be used to restrict passage through thewedge bore. Standing valves may be useful if it is necessary to pressuretest a liner.

It also will be appreciated that the description references frac balls.Spherical balls are preferred, as they generally will be transportedthough tubulars and into engagement with downhole components withgreater reliability. Other conventional plugs, darts, and the like whichdo not have a spherical shape, however, also may be used to occlude thewedge bore in the novel plugs. The configuration of the “ball” seatsnecessarily would be coordinated with the geometry of such devices.“Balls” as used herein, therefore, will be understood to include any ofthe various conventional closure devices that are commonly pumped down awell to occlude plugs, even if such devices are not spherical. “Ball”seats is used in a similar manner. Moreover, as used herein, the term“bore” is only used to indicate that a passage exists and does not implythat the passage necessarily was formed by a boring process or that thepassage is axially aligned with the well bore or tool.

While this invention has been disclosed and discussed primarily in termsof specific embodiments thereof, it is not intended to be limitedthereto. Other modifications and embodiments will be apparent to theworker in the art.

1. A plug apparatus, comprising: (a) a wedge comprising: i) an axialwedge bore, ii) a seat defined in said wedge bore adapted to receive aball, and iii) a tapered outer surface, said tapered outer surfacedecreasing in diameter from the upper extent of said tapered outersurface toward the lower extent of said tapered outer surface; (b) asealing ring received around said tapered outer surface of said wedge,said sealing ring having an axial ring bore and being radiallyexpandable; and (c) a slip comprising an axial slip bore, said slipbore: i) providing said slip with a tapered inner surface, said taperedinner surface decreasing in diameter from the upper extent of saidtapered inner surface toward the lower extent of said tapered innersurface, and ii) being adapted to receive said wedge along said taperedouter surface of said wedge; (d) wherein said wedge is adapted fordisplacement from an unset position generally above said slip to a setposition wherein said wedge is received in said slip bore along saidtapered outer surface of said wedge.
 2. (canceled)
 3. The plug apparatusof claim 1, wherein said sealing ring includes: (a) an annular ring bodycomprising: i) a tapered ring bore complementary to said tapered outersurface of said wedge, ii) an annular inner groove defined in said ringbore, and iii) an annular outer groove defined in the outer surface ofsaid ring body; (b) an inner elastomeric seal received in said innergroove; and (c) an outer elastomeric seal received in said outer groove.4. (canceled)
 5. The plug apparatus of claim 1, wherein said sealingring and said slip are adapted to expand radially from an unsetcondition, in which said sealing ring and said slip have nominal outerdiameters, to a set condition, in which said sealing ring and said sliphave enlarged outer diameters, as said wedge is displaced from its saidunset position to its said set position.
 6. (canceled)
 7. The plugapparatus of claim 1, wherein said sealing ring includes an annular ringbody constructed of a sufficiently ductile material such that said ringbody can expand radially to its said set condition without breaking. 8.The plug apparatus of claim 1, wherein said annular ring body isfabricated from plastic.
 9. The plug apparatus of claim 8, wherein saidannular ring body is fabricated from plastics selected from the groupconsisting of polycarbonates, polyamides, polyether ether ketones, andpolyetherimides and copolymers and mixtures thereof.
 10. The plugapparatus of claim 1, wherein said annular ring body is fabricated fromplastic and has a elongation factor of at least about 10%.
 11. The plugapparatus of claim 1, wherein said wedge and slip are fabricated fromdrillable composite materials.
 12. The plug apparatus of claim 1,wherein said ball seat is located in said wedge bore such that when saidwedge is in its said set position said ball seat is situated axiallyproximate to said sealing ring.
 13. The plug apparatus of claim 1,wherein said ball seat is located in said wedge bore axially below theupper end of said wedge bore.
 14. The plug apparatus of claim 1, whereinsaid ball seat is located in said wedge bore such that when said wedgeis in its said set position said ball seat is situated axially betweenthe upper end of said sealing ring and the lower end of said slip. 15.The plug apparatus of claim 1, wherein said ball seat is located in saidwedge bore such that when said wedge is in its said set position saidball seat is situated axially below the midpoint of said slip bore. 16.The plug apparatus of claim 1, wherein said ball seat is provided by anupward facing tapered reduction in the diameter of said wedge bore. 17.The plug apparatus of claim 16, wherein said tapered reduction indiameter is approximately 15° off center.
 18. The plug apparatus ofclaim 1, wherein said tapered outer surface of said wedge is atruncated, inverted cone and said tapered inner surface of said slip isa truncated, inverted cone.
 19. (canceled)
 20. (canceled)
 21. The plugapparatus of claim 1, wherein said slip comprises a plurality ofseparate slip segments, each said slip segment configured generally aslateral segments of an open cylinder.
 22. The plug apparatus of claim21, wherein said slip segments are aligned axially and, when said wedgeis in its said unset position, circumferentially abut along their sides,said slip segments thereby providing a substantially continuous saidinner tapered surface of said slip.
 23. The plug apparatus of claim 1,wherein the upper end of said slip abuts said sealing ring about thelower end of said sealing ring as said wedge moves from its said unsetposition to its said set position.
 24. (canceled)
 25. (canceled) 26.(canceled)
 27. (canceled)
 28. (canceled)
 29. (canceled)
 30. (canceled)31. (canceled)
 32. (canceled)
 33. (canceled)
 34. (canceled) 35.(canceled)
 36. (canceled)
 37. (canceled)
 38. A method of plugging aliner bore; said method comprising: (a) running a plug into a liner to alocation to be plugged; (b) setting said plug in said liner; and (c)dropping a ball onto a ball seat provided in a wedge of said plug.
 39. Aplug apparatus, comprising: (a) a wedge; (b) a plastic sealing ringreceived around a tapered outer surface of said wedge, said sealing ringhaving an axial ring bore and being radially expandable; and (c) a slip.